Personally, I'd like to see a system where there would be "generic" classes, but then specialized classes that a person can tree off of. Of course, this would require more than 10 classes, and so the likelihood of it appearing is nil.
But it's a system that EQII uses from what I've read, and it's been used to good effect in games like Final Fantasy Tactics. While the game itself is a hack n' slash sessions with some story occasionally interupting, the system itself was pretty slick. It went so far as to even provide base classes that only certain races could take. I actually liked that, as it added a cultural and physical limitation to the classes.
So a human could be a fighter, an archer, etc., but he could not become something like a monk or a summoner. Granted, I don't think D&D should have as many crazy variants as Final Fantasy had, but I liked the idea that classes branched out from each other, and you could learn a variety of skills from them.
If I had envision a class system, it would have something where the archetype was set (I'm not a fan of "generalized" classes unless I'm doing a modern setting... a fantasy world where I can't readily identify what it is people do is kind of boring to me), but then there were several "paths" available to them.
So a fighter could either be a generalist and receive bonus feats every other level, or have access to a tree of simple variants that swap bonus feats for a progression in a single weapon (weapon master without being prestige class), or a code of honor (samurai).
A paladin that could either go primarily as a spell casting route, or a paladin that has no "spells" at all to cast besides lay on hands, but other kinds of bonuses instead.
A monk (no one destroys my favorite class!

) that is less dependent on its static abilities that people sometimes don't even like seeing, and instead a distinct tree of system or "schools", some representing cultures that aren't even necessarily asian. Priestly monks, warrior fighters, vagabonds.
But four classes and just a hodgepodge of skills. That's being done by other systems. I'm not sure D&D would really benefit its entire fan base going that route.