Apologies to any who care (although I doubt anyone is starting on this post...) about it, but Tristan Alkai asked me to comment on this thread again since I re-emerged, so I'll be necroing this to respond to a necro. (The sphere of death waxes in power this night...)
Before I get started, a quick aside about "Xenosynthesis Energy", though; Personally, I would go for "xenoenergeia" or the like. "Xenosynthesis" would be specifically the biological process of metastasizing xenoenergeia/magic. (Lit. "Foreign/Unknown Energy") The term itself actually does a good job of encapsulating the idea behind Xenosynthesis/Xenoenergeia, however - that it combines magic with a sense that it is a type of science, just not one we know.
There's a LOT to get through. You guys sure love to talk even when I'm not posting text walls, myself. (Love you guys!) I'm going to start, however, with a few baseline topics, because they need to be addressed if this topic is to have any meaning.
Arguments can only be resolved when people agree upon what the goals are, and what the facts on the ground are. If one person is trying to solve 2 + 2, and the other is trying to solve 5 - 3, they'll never agree on the answer. A lot of this is talking past one another.
There's magic stuff down there. There is no way of getting around that.
Except there is.
You could just as easily do the opposite of making magic plantlife to match: you could change the magical animals to be less magical, then make realistic underground plants. I don't think amethyst men etc. really add much to the game anyway that slightly different sensical versions wouldn't, this doesn't seem like a big sacrifice.
The problem with basically all of GavJ's approach to this thread is that its goal is to argue that DF doesn't need magic. That the magic can be retconned away, and that we can then go back to playing the low-magic DF that DF has been in the past, and that a lot of people have grown to love.
I'm honestly quite sympathetic to that, and I look forward to the magic stuff with some trepidation, myself. However, that's not the purpose of this thread. That's not the purpose of DF, either.
DF, as the Cado story shows, was never meant to be Low Magic. It was
ALWAYS High Magic.
DF was always a game where you could find a magma river that had magma men hanging out in it. You could close your eyes and kind of go "LALALALA!" to pretend it didn't break the low magic feel of the game, but they were always there. HFS is a place you can just WALK into. The game's been growing more magical, with things like the shadow beings existing in another dimension, being able to cross over whenever it's dark outside because they're sympathetically aligned with Shadow.
The original purpose of this thread was to try to square the circle of a realistic farming suggestion with a world that had the capacity to walk off into alternate realms, speak with the dead, and use blood sacrifices to summon divine beings. Because that's what DF is supposed to be, and is going to be.
Arguing away xenosynthesis doesn't change that Toady wants to further DF's evolution into a high magic game, as that's coming anyway. What Xenosynthesis was supposed to accomplish was to say that, if this stuff is going to be in the game (and it is), then it should at least be, if you'll pardon a not-quite-word,
engineerable magic.
As you say, amethyst men right now don't add much to the game. Necromancers are something that exists completely in their own little realm utterly divorced from Fortress Mode except in that they keep spawning monsters on your lawn. You really can't do much of anything with them but to keep them in a pit and maybe let them out to raise some zombies on a goblin siege for the giggles.
I don't think we want whole cadres of dwarven wizards, either, but magic is going to be a part of the game, one way or another.
At the same time, water, magma, cave-ins, drawbridges, animal logic, minecarts, etc. are all powerful tools for the player, as they are all
engineerable forces within the gameworld.
The reason I wrote all this was to try to find a way wherein magic is something that isn't as plain and boring as getting a slab and suddenly having infinite zombie hordes or having wizards spitting out fireballs based upon MP.
We're going to have magic coming from alternate dimensions and sacrifices to gods and tomes of forbidden lore that give their reader the ability to walk into alternate planes, and even the capacity, according to Toady, to outright link your fortress map into a different dimension, so you can invade Heaven or something.
Every time you add a mechanic to a game, you add to its complexity. However, you can also add to its depth. When you add mechanics that don't work with the other mechanics, you prevent its capacity for emergent gameplay opportunities, which add drastically to the depth that a game has. DF is known for being so deep and having so many emergent reactions that Toady frequently has no idea exactly what his game is going to do, and that's because everything tends to be forced into a single "space" (or rather, spacial/physics simulation) where all the moving pieces interact with one another all the time.
What this thread is about is trying to make that connection of these magic abilities that just spring ad infinitum from characters powering their abilities ex nihilo deflates that physics simulation, and weakens the capacity of the game in general to be engineerable.
Xenosynthesis says that, rather than these powers springing up ex nihilo, they are the side-effect of what we already do in the physical space of this world. Hence, it's directly linking the power and type of magic in the game to the way in which you play the game, rather than it being arbitrarily decided by the RNG before you start playing.
"Random crap happens for no good reason," is not nearly as satisfying a game or a story as, "Your continued abuse of magma has caused Insel Shamshok the Flames of Loathing, to curse your caverns! The powers of magma course through the veins of the creatures of the deep! A magmaman horde now trods from the depths to beat at your door!"
(Jeez, and I thought I was keeping it relatively short... Response to Tristan in particular in a bit.)