Ok, thanks for the input!
Now, in a somewhat different order of things... I am somewhat tempted (after some in-game DF experiences) to make a mod based on HG Wells' "The Time Machine". Which would be "Morlock Fortress", or somesuch.
The basic idea is that the main playable race would be morlocks, which would be cave adaptated by default. I think they shouldn't have ranged weapons, in principle, but would still have siege weapons, and traps. They would have underground crops, but if possible I'd make them all prefer meat. As in, to the point of being unhappy without it. As in the novel, morlocks keep a civilization of sorts, and are pretty productive. Maybe there should be wild morlocks as well, as potentially hostile beasts?
Then there would be the Eloi, the wild ones would be huntable regularly, whereas the "civilized" ones would in principle trade with you. However, you can still kill them for meat, as they should be butcherable. They ought to be fairly weak and easy to kill. Perhaps the ones you trade with should be assumed to be their pseudogoverment and thus keep some semblance of bodyguards with bows and such.
There would also be an alien race which would trade with you, but might or might not be annoying. Sort of an elves equivalent.
Finally(?), I'd add in a "high men" or "sleepers" or something like that, faction, which would be ancient, un-devolved humans, which would be hostile towards Morlocks by default and would lead sorties against you. They'd have advanced, pretty deadly, weaponry. (BTW: is it possible to make it so that their weaponry is usable even if you cannot produce it?). They'd also be stronger than morlocks, although possibly slower. They ought to have some building destroyer units (tanks?)