I had a curious thought recently....
Well, a number of them, the first being:
I'm not sure if Toady will implement trading with subterranean tribes or not. Good question to ask.
Then another, as I realized something:
They plan to implement the option for a player to let a fort keep running. Instead of abandoning and ruining the fort, it will keep going, running as if on auto-pilot. They also plan to implement the option to retire in player forts, similar to quitting in a town/village.
Well, what about companions? I mean, you can recruit normal people, of all races, of many forms, and you can even recruit Animal People....
So, there's having your companions go insane/wild, but what would be more awesome, is your companions, join the society you joined.
The only strange thing is how they'd code it to where you can having citizens of other species. We already have nobles if I'm correct, who can be necromancers, or goblins, so they could classify them as Migrants, or, a new noble class known as "Dignitaries" or something else.
I think it'd be interesting at least.
Reproduction would be weird though, I don't mean cross breeding, but would they use egg laying still? Or would it be modded?
Which, could end up interesting, say your fort becomes Cave Swallow Men.
Imagine making a small village/city for them, placed atop a set of supports, or other constructions. If enemy raids couldn't get up there, and if building destroyers don't target it to topple it, you could have your dorfs wiped out completely.
Thus resulting in a Cave Swallow Men Fort, up in their nice nestbox/bird house.
I mean, if you seal them in a self-sustaining sort of world.