Couldn't you read the ROTJ celebration footage as flash forwards? I find it hard to believe that news could travel fast enough for the Bespin/Coruscant/Naboo/Tatooine stuff to be literally be happening concurrently with the festivities on Endor, so what's to say that those scenes don't happen weeks or months later (as opposed to the handful of days most people seem to assume)? If we're flashing forward either way there's no reason a short increment of time should be more valid than a longer one. And Bespin is the only planet shown that has anything to do with this Uprising game. I think that as long as there isn't a definite timestamp on that shot, fitting the new game into the timeline isnt a huge stretch.