We should have the ability to create religious institutions, with support from the game engine. The idea is that we have an extensive type of claim, similar to a kingdom's, but different in how it's expanded and maintained. I'm sure this concept could be applied to kingdoms themselves, but it might be more interesting if kingdoms and religions are made different things.
Religious institutions (RI) shouldn't give passive bonuses or receive an XP tax from members since that's already covered by kingdom mechanics. Instead, they should rely on active behavior like player worship in the form of XP or random item sacrifices (like the old numen). These sacrifices would be made in shrines built by the RI representatives, and would give the worshiper a temporary bonus in return.
The nature of these shrines would vary and could follow the old 12 belief bars, allowing shrines for life, death, industry etc. The RI itself, I think, could choose any combination of the 12 beliefs upon its foundation, to give us more diversity and reduce possible exploits, and the resulting quality of the sacrifice /worship bonuses would then be related to that combination (for example, a RI focused on "nature" would return better bonuses than one focused on "life, nature and civilization ". Alternatively, a RI with multiple focuses could also have bonuses that other RI's don't).
The sacrifices could also give the player other kinds of things, of course, like a temporary unique combat move, additional AC value, improved fate formula, and so on.
I feel the game is too linear, everything goes from 1 to 2 to 3, from personal claim to village to kingdom. It would be nice if more dimensions were added to the social structure of the world.