AI Revolutions?

Has anyone seen the AI get a revolution? I don't mean seeing another faction emerge, I mean going from Absolute Monarchy to Republic, etc.?

Is it even possible?

Yes, but only once. I was thrashing the marathra (I have a feeling that was spelt wrong), they had 2 cities left and they became a republic. I did not see the rebellion army though.

I haven't seen it, but I'd expect it to be pretty rare, because the capitol will probably rarely have enough disorder to trigger a rebellion. The times I've seen outright rebellions have always been provinces with a school, where the "clamor for change" modifier overpowers a weak garrison, especially if a pleasure garden has been raided by an enemy. The AI almost always builds to a full stack in the capitol and is pretty aggressive about protecting the main province.

I've seen Spain, Sweden and the Marathra go Republic.