I haven't read all of this, so forgive me if something similar has been said.
I think it'd be neat if they did a subclass for each school for wizards. Instead of just having extra spell slots, maybe give them all cool abilities that work off of their respective school! Depending on what abilities you come up with you could even restrict them to having only spells of their school! Maybe too radical, but It'd be just an option anyway. I'd still wanna see the basic wizard we all know and love/hate.
Qmark on the wotc forums also brought up a neat idea.
Early access to spells. This would help make up for the narrow versatility of a single school caster. If that proved too strong, maybe limit it to one spell per spell level to be casted one level lower. Then you'd have class abilities etc as you level too.
Maybe make it like this...
Abjurer - Has Abjuration Spells, and class abilities based on Abjuration. They'd be very defensive, but could work.
Conjurer - Has Conjuration spells, and class abilities that enhance or work with conjuring things. I'd like to see summon monster of course, but maybe something to do with summoning good weapons too?
Diviner - Maybe some sort of Gish? Precognition to avoid incoming attacks etc.
Enchanter - Enchantment spells, etc etc.
Evoker - Obviously the Direct Damager caster! Would have class abilities that deal with enhancing that aspect. You'd also have some other tricks too like Grasping Hand etc.
Illusionist - Yeah
Necromancer - The Undead serve you etc. etc.
Transmuter - Would be FUN. Wizards that turn into dragons and eat their bunny rabbit enemies!
Universalist - your basic wizard. would have less cool stuff, but would have more versatility.
You could even still do the 3.5 specialist too, he'd just not have the cool class abilities of the mored dedicated wizards, but would sitll have some versatility.