Instead of an automatic check for peasants to mob the noble in question, I suggest it becomes a priest action. If the priest is in the region and has sufficient followers, he can whip them into a frenzy to attack the noble in question.
That could be a good substitute. I prefer having a passive effect, because it seems obvious to me that religion should have such effects but, if Tom doesn't go for it, I'd be fine having it as a priest action. It'd give priests a way to harass infiltrators.
Err... actually, abuse alert: priests would become key anti-infil defenses. Find an infil, fast travel to his location, mob him with peasants. Now admittedly that seems somewhat plausible from a medieval perspective (foreign assassin gets caught up in backlash by peasant zealots when a priest points out who he is), but from a game balance perspective, infils have been pretty nerfed it seems to me, not sure if we want to do so even more.
