What I'd like to see, is path of the Mage unlock spell professions, that would provide bonus spells to magic levels.
Like fire magic+ summoner= a stronger type of fire elemental at say Archmage
Earth Magic+ Mage= stoning spell
Some of the Book of Flames/Frost/Winds/Stones spells should those techs disappear should end up here.
Mage path is the strongest right now, so this would be a slight nerf, but an interesting nerf.
The three professions I'd use
Summoner= summons
Evoker= direct damage
whichever promotion gives mastery= other spells such as maledicts
If Stardock needs some ideas for other schools along those lines, I have plenty of ideas.