Alright, that's a lot of ideas. But umm...
About the catapults: does it destroy the stone when it's fired, or no? because if it didn't, then my masons and stonecrafters and mechanics will constantly be running out to grab some stone from the catapult firing range, only to come back with half a dozen broken bones and damaged organs.
About the economy: I know it isn't perfect, but I feel like my wouldn't be a real Dwarf Fortress game if I used something that took out a core game aspect.
About the poison ivy: That would be nice, especially if it was kind of a dominant plant that takes over everything like ivies do IRL. And considering some of the other things that dwarves eat/drink, it wouldn't be too bad. I can even imagine myself drinking a nice glass of Ivy Wine.
About the pumps: Heh, not only do I not know how to make and use pumps, but wouldn't it be a better idea to have the dwarves that would be pumping to be mining out my new bedrooms instead? and that way, they'd get legendary after a year or something, while there would be rooms for the immigrant dwarves that they wouldn't get kicked out of.
About the Purist-Modders War: I'm personally rooting for the modders, since I don't think modding the game is cheating. I mean, adding content (like a civ mod or a texture pack) changes the game in a desirable way. Sure it may not be the true Dwarf Fortress, but it's still fun and we play it for fun. But on the other hand, a mod that takes out something (other than a bug or exploit), like the Zero Rent:Yes tag, just doesn't seem right to me.
About the adamantine kittens: If you melted them down, what would you get? Adamantine bars or Kitten bars? Or both?
Anyway, thanks to all of you for the flood of replies!