The only thing I can think of is that the civ that has been excomunicated would lose the follower beleif and slowly lose the citizens that were tied to the religion.

The loss of bonuses followers - not a bad idea

yes I like it, good idea

here is a good idea;
if you excommunicate a civ, all the civs that follow your religion(and you) denounce that civ, which greatly damages relations and they also stop trading with the supposed civ simular to the new diplomatic funcions in the elections
ps: sub'd and will dl later

Thank you, I think so and will

Will it be possible for all religion followers to vote first before excommunication is imposed?

I recall a related mechanism in Civ 4, the Apostolic Palace. The prospect of a religion-based medieval "world congress"... :)

Perhaps add a happiness penalty to the excommunicated civ too.

About religious assemblies I think is an interesting idea, but it requires a lot of time to implement. Probably in the future