Once History is done, the world is kinda static. I'd like to be able to interact with the history to alter the nearby biome and landscape over time. In particular I'd like to be able to influence the world in such a way as to introduce challenges and challenging environments.
For example, what if I built a graveyard in an isolated spot and continually dumped bodies there? Maybe at first it could attract scavengers and carrion-eaters, and over time become a cursed place that attracted and/or bred undead things? I don't mean just "have graveyards spawn zombies" but permanently alter that part of the world as my Fortress progresses, such that in future Reclaims or Adventures, or even a fort located nearby, there is now an undead/evil/whatever region there.
Perhaps if I had extensive tunnels or mining away from my main halls (a nearby peak for example) and that section of mines or tunnels was never or rarely frequented by dwarves, it could attract subterranean wildlife or even settlements of non-dwarf-kind.
I was thinking that something like this could add extra history to the world for subsequent forts as well as letting the player fiddle with extra challenges and add new environmental effects. It would be a little like Dungeon Keeper, where various types of evil buildings would attract various types of evil- only in this version you attract them to fight them, not recruit them. Although... recruiting them would also be cool.
It would also be cool if trade routes generated roads on the world-map, and even more so if the player could send out expeditions to open new trade (or war!) relations which could then become a feature in the world's history. This would be a little like Pahroah and other city-building games, only much cooler because instead of "mission then you're done" you actually shape history.