I am also thinking that there is an interesting way to turn the patron deity/cleric relationship on its head. Suppose the gods were these patterns, these memes or urges that seek to impose a specific vision of law on the universe. All of those gods would be in a pitched war against chaos and arcane magic.
But suppose further that, at least in some cultures, a cleric is not the priest of a particular god or even a pantheon of gods. Suppose the cleric enters a trance state nightly and communes with the various gods she has in her spiritual rolodex. She can get healing spells from a healing god, protection spells from a god of protection and maybe sticks to snakes from a snake god. And when she is introduced to a new, more powerful god, she gets a higher level spell or a new spell.
In this relationship, there is no loyalty. I’m the cleric, I can channel your energy onto this plane, giving you a fleeting moment of existence and a slightly better toehold on this plane. If you have a problem with how I am using it, I can easily find another god.
This isn’t to say there isn’t some loyalty or even complete belief and loyalty in the gods. Paladins could be the true believers in this scenario (although I’ve never liked them). Up to you to play with it.
On my map, which is just a doodle at this point, there’s a country where magic use and lycanthropy are more common than anywhere else. I think here, the clerics freelance in this manner.
And if I am reinventing the wheel and there’s been patron-less clerics since 3e, please let me know in the comments below.