Civilization-modding related thoughts:
As mentioned, we could probably use a baby-snatching "Morporkian" race. Make them long-lived, but not immortal, and incapable of reproduction, so they'll establish a multicultural city and then die out. They should probably be fairly combat effective in order to defend it. I'm not sure whether to make the civilization aggressive - if it is, it might produce large Morporkian Empires that then fall when the Morporkians die out and the weaker babysnatched races have to defend them, but I wouldn't count on that.
The Morporkian civ probably shouldn't have civ leaders - Ankh-Morpork and its neighbors are city-states, after all. Site leaders should probably be limited to [MAYOR], although we can add more detailed positions like Patrician, Watch Captain, and guild presidents when the next version comes out.
Other potential civs:
- Dwarfs, of course. Be sure to take out all feminine clothing from their entity file and, in the next version, give females beards. Dwarfs shouldn't really require too many changes from DF.
- Trolls. For now, I could imagine something that lives in caves with military leaders like kobolds, but that are aggressive ambushers and siegers like goblins. Admittedly, that'd be difficult to pull off in the current version. I'm not sure there's a way to make them at war with the dwarfs and only the dwarfs. Possibly just make their ethics completely different?
- Uberwald. Make them humans that prefer forests, with standard nobles and no access to silver. Give them [RELIGION:ANY_APPROPRIATE_POWER], a preference for Dark and its associated spheres, and then make intelligent werewolves and vampires with those spheres and make them powers.
- Lancre: Another human civ. Fairly basic. Like mountains, standard nobles, kings and so on. Not very aggressive. Fairly boring, really, like Lancre should be.
- Klatch: See Lancre, but replace "mountains" with "deserts and coasts," and "not very" with "moderately."
- Omnia: I'd recommend going with the pre-Small Gods version, for no other reason than that it's more interesting. Human, no religion tags (so that nobody worships anything but the Great God Om) and military site leaders and civ leaders for now. EVERYTHING is unthinkable, except torture. Prefers deserts. In the next version, you can implement positions like the Cenobiarch and some sort of local religious leaders, probably deacons.
I don't really have anything in mind for Agatea and Fourecks at the moment, or for more esoteric places like Howondaland.
In the next version, we could also probably use the caste system to implement witches and wizards. There's no way to guarantee that every wizard will be the eighth son of an eighth son, but for the most part making witches and wizards rare human castes that are, basically, women and men with some additional powers each shouldn't be too difficult.