I'll definitely be buying 4th Edition, unless the previews reveal aspects totally to my dislike.
Even if it's a revised & consolidated 3.5 Edition, then it's worth it to me to not have everything spread out among so many books. If it takes a cue from the Star Wars SAGA game, especially in terms of streamlining the skill system and high-level play, then I'm even happier.
I don't see D&D ever losing the basic classes and archetypes, as that would change the game too much. "Talent trees" per class like in the new SW game would be most welcome.
The one thing that could turn me off completely would be a move to a "per encounter" allocation of spells and other abilities. I'm not really that thrilled about the "per day" mechanic as it is, as it's a pretty arbitrary and somewhat nonsensical limitation, especially for non-spell abilities. But "per encounter" seems pretty arbitrary and nonsensical as well, from an in-fiction point of view.
I'm remaining optimistic, however.