The problem that I referred to but you seem to have missed is that the player's economic activity is not necessarily in any way similar to how the AI would behave with the same population and resources.
Well, as I wrote earlier, you need to factor in sites resources, workshops and workforce. For realistic economy you need to keep database, which is tracing all transactions. For unrealistic economy you conjure from thin air with help of rule-set, but one based on dev's common sense. AI is regulated by ethics (an economy of the race) like players, so same economy/regulations apply to both. If player couldn't build high boots, then AI won't either. Even if player traded cups and mugs with caravan to get weapons and armor and build some sort of farm plot, brewery, kitchen and build tavern. AI is not obligated just to maintain those production lines, given there is overflow of migrant population. AI should go for balancing act, so site will not have massive emigration to new player's embark. DF is not a trade game. Only few embarks missing some resources.
Also, if you don't want always to play with one rule-set for goods, when conjuring from thin air, you can let AI to shuffle some ideas of products. Player maybe was producing 500 chairs to be thrown to lava, but AI can stop all production chains in when surplus of 10 items. Factor in rest of available untapped resources on site, create new workshops as needed and workforce available and conclude that there could be 10 further items of each sort to be in stockpile for the rule-set.
Ultimately player from another embark can add changes to the rule-set as well with existing mechanics of tender offer, by requesting some items (or groups of items, that would be an improvement to the existing system though) in larger amounts then those 10. Right now request goes in 1-5 stages, so how sounds +3,+6,+12,+25,+50? Though it would be conjuring from thin air, without database, specially in case of mining. Database searches and transactions could be speed up and be very fast. It just takes to learn few SQL phrases, which you inject into your programming. AI could take advantage of database to set up its own choices (clustering of examples you know?), besides the ones based on rules and react more intelligently. However you would need to put entire world in the database first to play with it from start too.
The thing is to let lose the site-2-site trades instead of civilization trading caravans. Here my suggestions about dedicated Trade Depots factor in, as solution. You see? Even if you conjure from air items, which are on a list.
So, you say factoring existing quantum stockpiles in is tricky by AI, as there are more goods then storage?
I am saying the opposite. That getting rid of quantum stockpiling means we need to take into account storage-space.
I see. This is not implemented yet in DF. This is true. Warehouses and Treasuries, which I propose, instead of stockpiles could magically take care about this QS future issue, solving it permanently. AI would need just have some free space and some blocks or logs to build some more of those magic QS-Depots. Stockpiles could be still useful for linking production chains. However QS-Depots would be required now for some refined items like prepared food barrels. Preventing vermin from spawning inside of them or entering into them for example. Alike Trade Depot does right now.
We don't have to worry about the regulations. The game mechanics are regulations, the hard part is making sure that the mechanics represent the functioning of the different economic systems, even when they coexist in the same society. For instance stealing, giving, taxes and commerce can all exist in the same society, but are mechanically different economic systems.
Currently only economy differences in DF, between races, are those based on moral ethics. Those do restrict which civ can build what workshops. Nothing else. So each set of regulations = an economy.
If there is nobody around the witness it, then there is no problem in a computer game with conjuring things out of thin air. The game will never be able to handle actually modelling the whole world economy as if it were fortress mode, so yes we are always going to be conjuring things out of thin air and nothing wrong with that as long there is nobody around to witness it.
What makes the present caravan a placeholder rather than an incomplete mechanic is that given the existence of different economic systems in the game, we cannot just model the effect of the player on the game economy *in general*. If the goods you sell to the caravan will never exit the economic system of buying and selling, then we can model the whole world by modifying abstract values at a site/civilization level in response to the player's behavior. What requires that we track the actual production, consumption and transfer of the goods is that there are other things like giving, taxes, stealing and so on that mean that we have to figure out where the goods end up.
If bandits waylay your caravan once it leaves the site, this modifies the whole economic situation since the goods are now part of the criminal economy rather than the legit one.
Why would you want to model player's impact on economy? Economy is economy no matter by whom or what it is resolved. In worst case scenario you have site bankruptcy and you just factor that case in.
Abstract model of economy is non-functional. Conjuring from thin air patches its gaping holes and makes it workable. So you are best with making the economy by setting up those regulations for each civilizations. At least then abstract economy model will be less fake. You will still need to conjure item from air to make it work, but it will feel to players more realistic, then right now with what goods Trade Caravans are offering.
To kick start world economy, you need just send in tax collectors. Let mountain-home collect yearly tributes from local sites. That's it. You don't need anything else really in DF. Just taxation. Trade Caravan already has existing donation system in it. There, whole economy was born like in real life.
About the rest of economics, which you may want in economy DF release:
-Dwarves using dispensaries instead of stealing items from stockpiles
-Dwarves earning money as wages/shares
-Embark creating currency and storing it in vaults
-Embark manufacturing requested and desired by Dwarves items at highest quality to get some of that coinage back.
You just use double book keeping here for check and balances. Store unsold goods in QS-Depots, stockpiles while with sold goods in chests, bags, coffers, cabinets and such. You keep on Dwarves info how much fortress owns them in wages and if it goes over the top (lets say 12 months worth?), then Dwarves will revolt or go to strike, unless receiving from dispensary owned them coins or desired items. You keep unspent coins in vault instead of dispensary btw. Keep in mind, that some goods like cloths, food and alcohol are workplace privileges for workers. They don't need pay extra for them. Rooms either. Though own personal chests/coffers/bags would make here some sense.
Interesting side effect of Dwarves owning coins. They can buy goods from Trading Caravans as well, so here having local shops for each embark, even your own, could be also an option. Metal can be rare, so financial flow should be bound to metal coins imho.
Caravans instead of traveling shop, could become just another safe goods transportation method. Then you can allow wagons and even ships in adventure mode to be bought by players. That would rise some fun.
Unless you strive to create ultimate multiplayer DF with player-driven economic system, then you can get away with conjuration from thin air using sets from lists. Else you need seriously consider using database. Actually you could create economy. Then create multiplayer. Then release some items from being conjured and allow them to be manufactured and consumed by players themselves. This is how Eve-Online step by step liberating items from their conjuration, created rich and thriving economic system. Both those steps of development would move DF to entirely new level of gaming. DF could start compete with big mmorpgs out there.
Though I would suggest always allowing for simplest graphics, which could allow DF multiplayer to be played even on mobile or tablet without much fuzz.
Big AAA titles go for flashy graphics and limit their player base.
PS. Unless you want just freeze with the rest of the world player's embark, after retirement. With all its oddities. I advise against that. Let AI think through and sort local economy first. Patch it and balance it as best it can. Then freeze the result. Though you would need to go through rules for AI, so no crazy stuff results from AI actions like 1000 Dwarven merchants, wagons scattered everywhere and such mayhem. Though, you always could try to consider imitating economy and even keep open gates for future development like multiplayer and real player-driven economy. So long you keep modular architecture and keep track of their interfaces, then there should be no programming chaos either.