(I don't really want this to be a 'suggestion', which is why I'm putting this in DFGD. Although admittedly the text has grown a bit in-between the original idea to post and the point at which I'm inserting this caveat. Given I think Toady already knows where he wants it to head, I'm really just riffing on the theme of the various musings I've personally had. Not intending to plagiarise anybody, but I suspect I reflect at least some
previously mentioned ideas, probably even one's I've never even seen, in amongst it all. Also, there is no real TL;DR; summary, for which I apologise. I'll leave it up to you as to whether you even start to read this monstrosity of a post, to which I've decided to add headings (now re-done as spoilers, as per suggestion... Yeah, probably better that way)
, and respondents should probably consider appling a lot of editing to the [quoted] text!)With Adventure Mode being primarily the roguelike 1st person game and Fortress(/Dwarf) Mode being (you might say, at least vaguely) Populous-styled in nature, but the promise that there be more wide-spread interactivity by a fortress (or site-building activities by an adventurer), I've been thinking a bit about how all the rest might work. Albeit that the following is mostly "how do you break out of Fortress Mode". I may discuss Adventurers switching to "Campground Mode" at length further down the line, but first I need to put my main idea down in some sort of order.
At the very simplest, something DFHack-ish (not that I've used it, so forgive me if I misunderstand that feature), except in a non-hack, fully integrated way. Indeed, "satellite sites" of a Fortress could as easily be spawned off as a new embark, the current fortress "not Abandoned", but just left in some sort of as-the-player-left-it state[1], and the intermediate journey could be fudged out, much as the initial embark travelling already is.
Sending out trading and/or militaristic groups from your fort could also be done 'ex camera'. Like the legal latin 'in camera', but you're confined to the room, and it all happens outside of your view. Organise a delegation of appropriately skilled/equipped individuals, and additional goods/supplies on a wagon or beasts-of-burden as required, and send them off the edge of the map. They'll encounter who-knows-what both at the destination(s?) and during the intervening journeys there (and onwards, and onwards, and onwards?) and back again and if they return you get to see how they fared and what they've managed to return with (traded goods, loot, a few less digits/limbs, etc).
On the other hand, I quite like the idea of what I'm going to call "Expedition Mode". Sending an expedition off uses the Travelling mechanism from Adventure mode (enforced, no tile-by-tile wandering along, primarily because we want to offload the fortress, not risk wandering in and out at will), but switches to a kind of micro-fortress (single-tile? 2x2 site?) when travelling is no longer occurring. That's either at the destination or when an Adventure Mode ambush would normally occur.
If ambushed in unoccupied territory, you find yourself facing the enemy and control your accompanying military escort as per your normal Fortress military, but can also arrange for your non-military to do everything from digging in to creating walls with carried/local material. At least so that they don't just run around in the way that civvies do. (You could set up burrows or other restrictions, but I think I'd rather have them running and dispersing than standing and presenting an unmoving target, if they can't quickly deploy some fortifications around them.) Basically, a reclaim/embark with pre-existing hostiles. We've all been there, with some wildlife immediately deciding to take exception to your dwarfy selves almost immediately. Well, this'd be the same only instant. (Thank Armock for the pause button, while you quickly get the attack/run orders set up...)
If successfully arriving at the target site, and it is unoccupied, it would be much as per a regular embark. Prospecting, wood-chopping, etc, can commence. For a limited time, though, as this is not intended to be a satellite fort in the above-mentioned sense, but a mining/logging camp to last for a relatively short amount of time (a few weeks of game-time, perhaps). Albeit one that could be revisited later on (from existing Fortress or a later one), or even rediscovered and reclaimed in a future Fortress Mode.
There's also the possibility of 'joining the dots' and using a succession of work-camps such as this to make cross-country gigaprojects. e.g. Isolating the tip of a major isthmus with Chinese/Hadrianesque Walls or setting up waterways and viaducts from unmanneddwarfed pumping stations at rivers all the way over to a desert fortress site. (Why? Because...)
If the target site is friendly (or at least not hostile, but occupied) you get to wander into their Trade Depot[2] or (if they don't have one) build your own temporary depot (logs+cloth=>marquee?) to which the locals may or may not send some trader and goods of their own for a bartering experience similar to now. The locals can pack up and no longer trade much as traders can pack up and leave when they visit you.
In Fortress mode, you can already choose not to trade any more, and while guest traders tend to hang around there's no reason why you shouldn't. In Expedition Mode, you'd just formally pack up and leave, much as you'd ignore trading in a Fortress and generally wish for the visitors to pack up and leave before the next Goblin siege arrives, so you can close your borders again.
Naturally, items that are $owned$ by the site (including items brought to your marquee, but not yet traded for, and items that you brought but which are now successfully bartered) won't be available to you. You should also be subject to seizure of items. I'm also minded to mention that you should not be able to make landscape changes (cutting trees, digging holes) without some sort of arrangement with the locals, or start being treated as hostile, as below.
Perhaps building something like a tailor's shop out of brought materials should allow you to act as itinerant workers... while you're there you can trade for cloth, create clothes from it with your Legendary clothesmaker (who would have just been bored if you'd left them back home) then trade this clothing back to them at a premium and in exchange for something you really want.
If the target site is in enemy hands, you've got a battle to fight, or at least guerilla action. You should initially be as hidden to them (until a patrol/lookout happens to spy you) as ambushing troops are to you in Fortress mode. (Adventure-mode rules regarding at least discovery of local landmarks should probably apply, although admittedly invaders into your Fortresses already have a fairly detailed knowledge... Or perhaps the whole point is that hostiles have scouted (at least the aboveground parts of) a site out beforehand.)
Bring enough troops/equipment and it might even be termed a Siege, though, with you as the sieger. Maybe the target site would be procedurally (re-?)generated as a locked-down site if they feared your masses, or they'd just rush straight out to take you on. Building or constructing siege-works should definitely be an option (assuming your siege engineers and/or other workers are not being pestered beyond the ability of your troops to defend them), albeit a potentially attention-grabbing one if you started off hidden to the locals.
We're also awaiting the mobile siege-engines that are have been discussed before w.r.t. Fortress Mode, so I could see you converting your wagon (would mean unloading it, first, though not actual deconstruction) to be a wheeled and roofed battering-ram, siege-tower or other such vehicle. Less mobile, there's the like of accompanying miners/carpenters/masons building a mini-fort of your own (something small and quick to dig and/or construct) to hole up in while you prepare, or to actively start bridging/sapping operations from as part of your attack plan.
Regardless of whether an occupied site is friendly or hostile, the forthcoming Thief role in Adventure Mode and the pre-existing thieves in Fortress means that you could have anything from pick-pockets (in otherwise friendly territory, to allow $Items$ to be taken, with all due consequences if it's not a clean-steal) to snatchers (if your civ morals allow you to do this, or as a form of pay-back or even regaining one's own 'lost children', albeit then needing programming/deprogramming to create/avoid Stockholm Syndromes when they are brought back to your home). Stealth skills are involved.
As for the running of your fort, Expedition Mode, unlike the "spawn a satellite, run the original on semi-auto" idea, might require that (assuming they can get back) there's no more than a single season of absence from the fort. How that is enforced, especially if multi-stage circuit trips are allowed, I have a number of ideas, among the least satisfying of which is that there's a form of count-down timer compared to distance from the expedition's home and it will not let the expedition go further than a certain (gradually decreasing) radius from home, and automatically sends them home (ambushes allowing) if time is up. Perhaps with a bit of "pack-up time" if they've set up a small mining station and have been mining and accumulating certain ores or other resources, but certainly a warning along the lines of the existing "The traders from OtherPlace will be leaving soon" mechanism. Only with themselves.
As for the home-fort running itself, while you're away, if it's something like a one-season limit it might even be best (at the expense of more playing time needed for a given amount of game time, but providing more interest for all that effort of 'repeating') to arrange that both Fortress and Expedition play is player-controlled. Not in parallel, but sequentially. Potentially in either order, but my current thinking favours Expedition then Fortress[3]. Controlling the Expedition, you know what the Expedition's initial intentions are, as you venture out into the world, but are expected to have no knowledge of how things are working back home, in your absence.
Whenever the Expedition is over (in utter failure, or just as you're about to arrive home), the off-loaded fortress is reloaded at the point of your initial departure (without the sent out expedition units/materials, obviously) and continues as normal. Should your expedition have already proven to have arrived home, it will occur at the appropriate time in the Fortress calendar and Ye Shall Rejoice! If your fort falls (or you actually abandon), whilst waiting for the expedition to return, you switch back to the returning heroes (if any!) encountering the desolation that is your defeated fortress, who then have to deal with what they find as per a reclaim. (Dead bodies, plundering invaders, clowns, lava flows, restless spirits/zombies, or... ...Marie Céleste like emptiness.)
What's trickier is how the game should perhaps handle the lead-time on reciprocal visits. If you're out 'visiting' an enemy's fortress, the game should be made to already know that the military elite (or penal troops) from that site have set off to try to wipe your home off the face (and out of the bowels) of the earth, and you'll either end up "ambushing each other" somewhere on the route between the two places, or arrive to find a poorer-than-normal showing by the opposition, then when the playing the 'home' leg of the bifurcated time-line, you find out why...
Expeditions could, of course, head out either overground or through caverns/tunnels. I'm not sure what mechanism would be used for working that out, though, especially given not all sites would have the suitable underground connectivity, there might be more problems with ambushes while Travelling and it really should take into account wagon-accessibility, albeit that it still lets you Travel over an 'normally' impassable river gorge at the moment while Adventuring. Still, it would require that you not have an Impassible Perimeter around your embark site. At the point in time that the caravan is expected back, at least, which is an element of philosophy that the Caravan Arc is supposed to address.
Also, if your Expedition has built itself either a work-camp or a siege emplacement without ingress, for safety, then if there's an enforced return schedule there should only be a limited amount of time afforded to you to open up so that you may wander back off the map (dealing with whatever hostiles you have been baiting from your battlements all this time, as you do so). Otherwise the entire expedition (gradually, or one-by-one) goes crazy from homesickness, or has some other reason to be no longer under your control and end up never going back home. Cue "rescue expeditions" (once the Fortress has been played long enough for the incident to have occurred to your off-map expedition). Or a form of feral fort that (now overdue) you are able to send out another expedition towards in order to retake, quash the rebellion in or just plunder the remaining treasures from in amongst the bones of your unfortunate first expedition...
It's a bit of a mass of a non-suggestion, I know, which is why I'm pretty sure I don't want to suggest it formally. But I have taken care to integrate only features that are currently (or imminently) implemented, albeit the occasional thing such as $Ownership$ needing reimplimenting into the Fortress-style playing field through the code already used in Adventure-type play. Also, no memory-worrying, because the inactive 'leg' is saved to disc for the duration (and a reduced-sized Expedition embark area will need less resources than your original megafort, anyway). No additional processing problems, because there's no actual need to run anything in parallel to the player-view in real-time, and neither do you need to up the game of site-management AIs to support all the diverse player-building and management strategies. Which is not to say it'd be easy to do, of course.
[1] Ideally not a complete stasis, and of course a player fort in the hands of an AI would, apart from impacting the new fortress site's FPS, be totally unable to deal with most player-built design elements. Let's just say that if the fortress is creating enough food at the instant of (or over recent history up to) the re-spawning, reproduction and continued thriving continues apace by dint of finding the fort richer in some yet-to-be-determined way, upon revisiting. If there are any pressures on the fort (sieges, attacks, hunger and thirst) culling and loss of persons/goods will have occured. But that takes a bit of working out as well. I'd say that you also can't pause the demands of a noble or moodstruck dwarf, and they will have gone into their relevant punitive or mad mood automatically, while you're swanning around at your new site. Perhaps if you can send goods back (or send an expedition of all/some of your settler-dwarfs back home, to re-establish original site playing) in time, you can avoid that. Otherwise it procedurally works out what will happen, and to whom. Perhaps based upon a snapshot of the pathable-to dwarfs/locations at the time of departure.
[2] And your entourage members who wander in and wonder why there's spots of 1/7th magma lying around the place, handily placed in a small room surrounded by drawbridges, can just shut up, 'cos there's absolutely no reason to believe that anything might be wrong...
[3] Fortress-then-Expedition sequencing has its own arguments. I don't like the idea that the expedition (only taking out to trade what it's been sent out with, but given a choice in what it trades
for) can miraculously and suddenly know that there's a sudden need for something like glass or sand, or no longer a need for the load of minerals it was originally intended to obtain, but then again the Fortress spirit (the
real continuity in the whole game, i.e. you) should perhaps not know anything until the caravan or taskforce is about to arrive about whether or not it
will be returning, and in what condition. However, only once you've run the expedition trip through do you actually know how long it should have taken for the expedition to return, unless you force the caravan to stay away until the point at which you've already played the fortress to, or enforce a strict "There and back again" trip.