[@Kejmur] I like this idea. I would think that those born with mana would take on one school of magic- thus permanently aligning their mana to one type of magic (blood magic, primal/nature, etc.) Perhaps some sort of writ of passage would complete this transference. I would think that mages in most societies would be required to train their magics (with certain magics being forbidden). 

Perhaps when it comes to ki and whatnot, some people have 'latent magic' which is more flexible, but also "less powerful". This way we still have those in the world without any kind of magic, some who have the potential for magic, and those who are 'destined' to use magic. In this way, we can think of magic and mana as existing on a spectrum rather than the have and have nots.