Historically I can think of 3 revolts which I had in mind, the English Peasants Revolt of 1381, the Jacquerie, and the Flemish Revolt 1323-1328. All of them had significant impact, the first causing the death of several councillors and nearly succeeding if not for the monarchy secretly murdering the leader during peace negotiations, the second caused a ton of chaos though I can't remember why it failed, and the third succeeded, with Flanders some kind of independent peasant republic (led by a rich farmer) by 1325. Flanders was suppressed, of course, fending off one army from the king of france and falling to the second.That would be a pretty cool idea. I don't know how the heck the coding for that would be like, although it would probably be something similar to the Hansa (at least how the republic pops up). I also don't know how really workable that would be - historically, if I am correct, many of the peasant republics got offed pretty quickly. I wouldn't want to have them arise ahistorically, that is, and I wouldn't want it to be a gimmicky thing. I think it would be cooler to implement rising republics in general, where certain regions meeting certain criteria could have a republic pop up, and different circumstances would lead to different styles of republics. So basically what I'm thinking is that a "peasant" republic might be good, but it'll basically still arise similarly (and perhaps function *somewhat* similarly) to other republics, only with different prerequsites. If that makes any sense? I've put rising republics on my to-do list, anyways. Probably in the far future, though.
I think of it as a way of making rebels in provinces more dangerous than burning a few buildings and maybe killing a few peoples. It definitely shouldn't be a gimmicky thing, but a rare event I agree. I really like the idea of different types of republics, as currently they're much too straightforward. Either they're the 'conquer all the coasts and become insanely rich' type or the 'vassal and therefore unable to expand much' type. Personally I want more republics which aren't trade-oriented and republic flavour like that one guy who led a revolt in Rome against the papacy and tried to re-establish the Roman Republic.