The sorcerers made me think of Domain Wizards, for some reason.


As for wizards, perhaps you could just replace the whole thing with a generic Mage class with slightly different skills/capabilities for each sphere/domain.

Like how Psion works. You could have a limited list of generic spells they may learn, in addition to being able to learn spells of the school they specialized in.

Examples: Mages must specialize in a single school at level one. They gain no bonus spell slots for said specialization, but they also do not have to select prohibited schools. Mages may only scribe spells into their spellbooks from the generic spell list or spells from their school.
Mages may select an additional school of specialization at level five, plus one every five levels after that.

That would give you five schools to select spells from by level twenty.

Not sure how that would work out balance wise, though.