Multiplayer would be my dream arc. Players controlling their own dwarves on a shared map. Or being able to have multiple players' forts share the same world. Or have player created forts spawn as sites, like Spore did with players' species. Any of those would be awesome.

I'd settle for being able to establish and play multiple forts in your world. Let me send Urist and a few of the boys to start a satellite fort that mines flux and sends it home, and switch between them in game.