The biggest change will
probably come from an upgraded screen. I've seen random acronyms thrown around the Internet (such as
IGZO) that should help reduce the weight by reducing the ridiculous backlight needed for such a dense screen, which also shrinks the battery needed to power everything.
As for multi-user stuff, I would imagine that Apple has considered it, but there are quite a few questions that go along with implementing it. The biggest one is probably how do you handle other users? Google treated it like a computer and lets things run in the background. That isn't as much of a problem on iOS given the limited multi-tasking, but there's still background tasks remaining in memory. I would imagine that they would simply give preference to the current user's tasks over any other user's tasks or simply require logging in as another user to log any other users out. Most apps save their state to NAND anyway.
EDIT:
Some articles even seem to suggest IGZO as a done-deal for Apple, but when will we see another iPad refresh? Will Apple refresh it again in March or wait until October again?
http://articles.chicagotribune.com/...10_1_igzo-screens-igzo-displays-display-plant