Mm...So long as the religions are taking gold from the realms, rather than creating new gold sources, I see no difficulty with this. I'm envisioning a Theocracy with a strong, wealthy church and nobles who gain most of their funds from religious grants...I don't think the balance would be an issue so long as the estates, like all estates, can be reclaimed at will by the lord (while triggering the same unrest as trying to close a temple, say) and don't produce any more gold than they would for the realm.
