I am a 4E fan, and don't really think DND Next at this point is headed to be a replacement for 4E for me, at least. However, I think I could see myself being pleased with DND Next as an alternate game with a different play style, which could also be enjoyable. I did enjoy playing 1E, 2E, 3E and 3.5E when each came along.
What I'd like WOTC to focus on in creating DND Next is not so much creating a perfect balance of mixed editions, which could actually turn out to be less fun than any of the other editions. Instead, given the direction they are taking, I'd rather they focus on creating a good solid balanced game, fun for its own sake and balanced on its own terms. They need to conceive of their core game design phylosophy and stick to it. It seems they are basically going for a 1E/2E style with some refinements and advancements, kind of like an alternate evolution of the game, as what might have been 3E if different designers worked on it.
Though if there are design elements and ideas developed for 4E (or other editions or games) that fit into that design philosophy, they should incorporate those even if they are different from 1E/2E.