In the past we've floated the idea that during auto de fe's, RTOs, and persecution of heretics there "Martyr" subclass participates more directly in the violence than a normal priest. This boosts the chances of the effort succeeding but also carries a risk of the priest being wounded or even killed. I personally like the idea a lot. I might also add that a martyr could be more resistant to being attacked by the followers of another faith, but if wounded may risk dying. Also perhaps there can be some function where if a temple is attacked and a Martyr is in the area they personally lead worshipers and temple guards in defense of the temple, with the same rule of making it harder to destroy or loot the temple but with the risk of the Martyr being wounded or dying.
I've also floated the idea of Martyrs being able to give bonuses to faithful nobles during battles.
