As for classes: I'd like to see the number of core classes reduced to the Core Four, and the number of subclasses increased to encompass all others. Artificers, Bards, Psions, and all other arcane subclasses like Arcane Archer and Trickster, should be subclasses of Wizard. Druids of all circles, Warlocks of all pacts, and Paladins of every oath should all be subclasses of Cleric. And so forth.
Sadly, I don't see this happening. The trend is to create more classes AND more subclasses, thereby creating a desire for more books, which generate more sales. I get it; they gotta make that money and I want them to be successful. But as long as I'm dreaming about the future editions of the game, I might as well dream big.