On the one hand, I don't want them to show everything at once, but on the other hand I want to see a fair amount. Just so there is a little bit more we can go off of when speculating what the games will have in store.
I'd like to see the starters, and if they all received Megas I would like to see them, too. A, "Remember how Blaziken got a Mega Evolution in XY? Welllllll..." kind of deal.
If they are basing the new protagonist designs off of Brendan and May (which I think they will, but time will tell) then I don't see any reason for them to keep them hidden from us. Wally's redesign might come a bit later, but the protagonists I can see being revealed right off the bat.
Maybe no Gym Leaders...yet. But since it's gameplay footage, and we already know what battles look like thanks to XY, I'd like to see a town or two, and a route featured. Of course some battles will be welcomed, but I'd like a little more focus to be given on showing the actual locations. Hopefully that happens.
I want to know what's up with the Kyogre and Groudon on the boxart. I don't want them to take the "Mysterious Mewtwo -> Mewtwo Awakened -> Mega Mewtwo -> Mega Mewtwo Y" approach like last time. Just tell it to us straight, so we know exactly what they're supposed to be.
I don't want to get my hopes up, since I have no idea how long this footage is going to be. What we originally got for XY was some battles, the starters, the legendaries, and a little bit of location...but those were all-new games with nothing for the basis--they had more to keep hidden. Since RSE already exists, there's no reason to hide the things we already know about. Unless they're going to do something crazy-new with the mechanics, I can't imagine them focusing on anything else during this presentation.