So far I've seen lots of things that we're pretty sure will be in E3, but here is a few things that I would really like to see explained.
I'm sure there's a bunch of EU junk about the imperial dignitaries, but i would really like to see some explanation of who they are. I mean no one, not even vader, had that kind of access to the emperor. Plus they both looked to be several zillion years old just like palpy. It would stand to reason that they must be very close friends and most trusted advisors. However, Palpatine is already a very old man in E2, and still, there is no sign of these guys. Maybe he hides them in the closet or something. It would have made sense to see them hanging at his sides in E1 & 2, but instead it is mas amedda and others. I'd just like to see some reference to these mysterious people and understand why they have higher clearance than any imperial under the emperor.
In light of the above, it would also be really cool to see the royal guards actually do something. They are supposed to be the baddest of the bad -- the most elite troops in the empire. If in E3 we saw them in action it would really help understand their capabilities when you see them in ROTJ.
Finally, after watching the SW movies recently, I noticed that you really don't see a whole lot of aliens in the OT -- Except for the cantina and jabba's palace. Those locations are, of course, on an outer rim world. But there are no aliens in the empire, in bespin, and few in the rebellion. In the PT, most of the jedi are aliens, so I was wondering if Palpatine had to exterminate lots of aliens to make sure the force users would become extinct -- or maybe he just enslaved the aliens as he did the wookies??? Anyway it would be interesting to see some sort of explanation for this, too.