Three ideas, all of which might be fun, Fun or just plain horribad:
Dwarf Fortress Mafia: Vanilla Mafia, except all roles have dorfy names. Vig -> Hammerer; Assassin -> Snatcher; Townie -> Dwarf; Mafia -> Goblin; Doctor -> Surgeon; Cult Leader -> Cat; Survivor -> Human Merchant; Jester -> Elf Merchant; and so on and etcetera.
Initial flavour being that Urist McDuke was found in his room having suffered an Unfortunate Accident after Mandating the production of a full set of Slade furniture, and since this couldn't possibly be the work of any dwarf, you have to start looking for sneaky gobbos.
Bastardness can be added to taste.
Not really a new gametype if it's not bastardy, then. Flavor can be interesting, but it doesn't make the game unless it's explicitly designed to.
We did have a DF game once. The idea was that the players had to keep the fortress running, supplying food, fighting off elephants, etc, in addition to rooting out the scum. I forget what happened to it.
Mess o' Masons: Everybody is in at least two Masonic Orders. One (or more, depending on the size of the game and bastardness of the mod) of said Orders being the scumteam.
Interesting, but I'm forced to wonder just how much of an impact this would have. Unless town began organizing themselves in an attempt to break the setup, wouldn't most mason groups just ignore each other, since talking to each other privately usually wouldn't have any advantage over saying it publicly?
Lynch the Lynchers: A single serial killer and a bunch of townies. The catch: All the townies need to off both the SK and another townie to win. Game over when the SK buys it. The trick: D1 massclaim can reveal the SK, but if the SK is lynched D1, everybody loses.
I like the concept, but it's got some major execution problems. D1, what happens? Everyone tries to lynch their target. How do you get any kind of consensus? Do a handful of townies make a gentleman's agreement to dispatch each others' targets, then hunt down the SK? Do some people volunteer to lose?
Sure, everyone could keep their target secret and pretend they're looking for the SK, but why bother? Everyone knows they're not actually looking for the SK unless they've already hit their target, and nobody wants them to find the SK unless they've personally hit their target. It's also not like knowing who everyone else wants dead helps all that much- you might become a target once your victim knows you're gunning for them, but honestly how much are they going to care? If you're able to lynch them, they're obviously not able to swing the lynch where they need it anyway, and if they're able to lynch you, you can either swing the vote to your actual target anyway or you already have so there's no reason you'd care.
So, yeah. Needs a lot more nuance to be viable.