If they were going to have each civ create its own religion, then I would prefer them to have real religions, so Greece would have the Hellenic gods, the Egyptions under whatever their gods are known as, and each civ having its own religion. The religions in cIV can still be included, but they'll each be tied to a civ. Thn you have to sprea your own religion to other civs and try and convert then to your religion. This could lead to the introduction of a religious victory, where your civs religion is in 80% of cities, like in LoR.