I would love it if they did this, be a good way to cut down on piracy as well if the apps you downloaded had to be tied to your iTunes account. But I don't think I'd like it if you had to buy the apps from iTunes, that would be silly and irrelevant to iTunes in general, but I would like to see it, like Steam I guess, but for general applications rather than games.
Imagine downloading Final Cut Studio though, 60GB 😱