It seems like this unfairly nerfs blaster wizards in that they have to stick to a theme (such as fire spells), thus limiting their use against fire resistant enemies. At the same time, it does virtually nothing to God wizards, whose theme is "buffing/debuffing" (I consider BFC to be a kind of debuff). It also seems overly restrictive, especially to certain themes - for example, there are only 3 Wiz/Sorc shape changing spells in the SRD (Alter Self, Polymorph, Shapechange). What other spells can a "shapechanging" wizard learn?
I agree that primary casters should be brought down a notch or two in power level for most campaigns. I think forcing a specific theme onto casters is a bit heavy handed though, at least in certain cases. Instead, how about this: Every primary caster - that is, everyone with access to 9th level spells on their class list - must give up access to one school of magic (not divination) without gaining anything. If you want to make a specialist wizard, you must give up another school, and BOTH of your spells learned per level must be of your specialist school. Or, you could do it like older editions, and say that by specializing in one school you automatically ban its "opposed school." For example, if a wizard wants to specialize in Illusion, he automatically bans Necromancy, he doesn't get a choice. You could even combine both of these options.