I'm A Banana
Potassium-Rich
I like the idea of an inbaked part of the character (so not magic item) that can be strived for in game and given as a reward in game.
3e did it with prestige classes, 4e did it with the special powers that were inborn instead of magic items (boons). I would love to see a mix.
If you go to the mountain of the high master you can learn at his feet, and when you do you have access to something that no one that didn't do that has access.
I could easily see 4e-style boons killing Prestige Classes that are too big for feats and taking their stuff.
I'm thinking even Artifact-level boons that task you with certain quests or responsibilities.
Gameplay-wise, they work like a magic item: a reward for a quest. Only rather than a +1 sword, the reward is a +1 to all attack rolls...or somesuch.