I would like a lot of WotC stick to a new philosophy and learned from their passed mistakes with 3E.
CORE BOOKS which introduces all that is important and expansion books which further define the material already introduced by those core books. And no new classes in those books, people who are interested in playing a concept not yet introduced by those core books could try to retro engineer new classes before their official releases in a new PHB. But that's life, like the Rolling Stones track -- "You can't get all you want!" -- the 1st year.
What I envision the approach will be:
1st year:
PHB1
With 2-4 classes for each new power sources (which would eliminate entirely the 3 classes per splatbooks of 3E): in this case it seems that it will be Martial, Arcane and Divine.
Martial Power: Expansion Book no new ones
Arcane Power: Expansion Book maybe 1 more: sorcerer
Divine Power: Expansion Book maybe 1 more: ?
As we can see, they seem to emphasized this approach by specifying its a power book. Which will expand further on how this power source work, and what are the links for the classes. Is the ultimate goal of a class is to be the outsource of that power and how they will fulfill their destinies? There is a lot of material that need to be further defined I think but for reason of space they couldn't state every available paragon paths and epic destinies with all their feats and powers for each classes in just the PHB1.
Maybe we will see that approach for the 3 first years. Maybe not. I would just like it if they would be a little bit less secretive about the future of the game. The only reason I see is that it is in a competitive market and they seemed to suffer from the third party companies with loss of sales. It is not that the system was perfect, far from it, but they were loosing big time the last years. The only reason is that they thought the third party would provide only adventures which was not the case, at all! They expanded as much as they could so they could be seen as the one offering the biggest on anything, but they spread so big they lost it completely. Now, they won't make the same mistake twice because the customers will stop trusting WotC entirely and never comes back to D&D, that is what is at stakes, that is why they are so secretive, because its either win or loose big time.
EDIT:
Another reason I see it that way, 30 levels per classes seems to be too big to be defined entirely, so the PHB will touch a bit on the last 20 levels but will focus on a strong Heroic level introduction.
This is all speculation.
