Make religion members able to give flag something as "heresy," like vulgarity, and it automatically goes to the religion's elders, who rule on it anonymously. i.e. "the lesser nobles are grumbling that you've started to stray from the One True Path"
I like that. Ideally, the effect would be that the noble in question would not be seen as faithful by the majority; therefore for example the peasants of his region would start again to be unruly, as if he was a pagan, or for a priest his influence would wane.
Allow religions to declare characters anathema, whereby they may have a random chance of being assaulted by peasants in areas where that realm is dominant, especially if they're a courtier or something. Obviously the number of anathema persons should be capped, probably as a ratio of the members or priests of a religion.
Two words:
Bowie Ironsides.
This sounds like a very fun mechanics.
