I'd love to see that take on Divine spells. Perhaps have an open world game where your mana represents your favor with the God you're channeling. You replenish it not with items, but by doing things that please the God, as you said. Another neat idea would be to have the cost of divine spells go down significantly when wielding them against the god's sworn enemies. A cool idea would be to have you face off against a high priest of a rival god and then have both gods instantly grant their channelers with all of their powers and unlimited usage of them until the battle is over.
You could even have someone of multiple faiths who tries to balance his devotion to multiple gods so he can wield a variety of divine spells. It would provide for an interesting incentive to behave a certain way throughout the game, since many of your actions would either please or anger the many gods.
You bring up tabletop RPGS, but I'd argue they're part of the problem. Especially starting with 3rd edition D&D, where magic was codified into a reliable science and technology with clear-cut rules. There wasn't really a sense that magic was some esoteric, forbidden lore known only to a select few, and often at great price. Rather, it's something you can buy on a street corner for a few hundred gold pieces.
I played 2nd, the way it tried to portray magic was a horrible mess that was totally unplayable and created serious dissonance with the fact that the players *do* have easy access to magic in their party members, yet the rest of the world doesn't.
If you want to ado a thing where magic is something largely inaccessible rather than treated like everything else in the world, you can't also hand the PCs magic powers of any kind.
Edit: and then I realise this is thread necromancy, why does Escapist keep recommending year old content to me?