For the most part, I think magic can be simply narrative: Magical actions are narrated as such, provided something justifies it (usually a high concept) and are resolved using Approach rolls as normal.
In the source material, magic of different kinds do not play nicely together; it's a key plot-advancement tool, in fact.
I think magic is going to be of two general types, mechanically speaking.
1) A high concept or other story element justifies using magic to apply rules in an unusual way (allowing narration to justify rolling Clever on an action that would normally be Forceful, or making an attack that normally wouldn't be possible).
2) A stunt allows rule-bending or bonuses with a magic flavor.
So far we've seen a couple examples of the latter.
In short, I think that FATE is ideally suited to automatically balancing a magic system without adding subsystem mechanics: if the magic's power and scope is driven narrative, FATE already does it.
