I think the wizard will remain a generalist, but not in the way 3e's was.
In 3e a wizard had access to ALL magic that was labeled arcane. So a wizard could learn the best from each school with no problems at all, and often did. He's switch from dominate monster to horrid wilting to moment of prescience to magic missile to haste to phantasmal killer without a rhyme or reason, other than those were arguably some of the best spells in their respective schools.
The side effect of this was those signature effects came at high level, or at high cost. To balance summoning against fireball, you had to weaken summoning. To make dominate not overpower haste, dominate had to be much higher level. In essence, spells always had to balance against the "best" of their other respective schools.
Now, imagine that there is not just one arcane "I can do everything class" but a true generalist. He gets some of the best signature abilities from each class, but not ALL of them. So he might be able to raise undead, but not with as much variety as a Necromancer. He might have some summoning magic, but a conjurer will summon stronger stuff eariler. He can charm the guard, but the Enchanter/Psion can dominate him and then erase his mind.
That will open up room for such classes to a.) have a niche and b.) not bump up against the wizard who can do the same role effectively. The necromancer class might be able to raise an undead army easier than the wizard, but he's not going to have access to as many cool buffs or charms that allow the wizard to be versatile. That summoner's monster horde rocks, but he has little in the way of directly damaging his foes. The Enchanter might dominate his enemies, but cannot teleport his allies very far.
This leaves the wizard in the role of true generalist (with a slight edge in damage magic) but opens up room for summoners, necromancers, illusionists, enchanters, shapechangers, and swordmages who have unique spells and spell lists that balance against the wizard by being stronger in some areas but weaker in others.
(It also allows the classes themselves to become more versatile with talents and skills and such)