With a surge in the popularity of these "What do you want to see?" threads, I propose one more, albeit a slightly different one. This thread is not for what do you want to see, but as the title says, what do you expect to see? You must give your reasons as to why you believe this. I'll go first.
Many believe we'll get a Jabba's Palace box next. In other threads, I have explained (or agreed) why thematically I don't believe this would work. That point has been debated much already, however, one point not yet put forward is not one that is thematic, but rather, deals with expansion of the game as a whole. We just received BG which came with two new types of Mercenary units inside, while containing no Imperials (I know we got them through the expansions.). I would imagine that it is undisputed that Jabba's Palace would not have Imperials. So we must ask ourselves, "Would FFG give us two expansions in a row with no imperial figures?"
The next is Endor. This one, I think holds a little more water, however, I believe the content required could not warrant a big box, which is why I believe it could be the next small box.
So next we have Rogue One. This would be my expansion of choice, but I doubt it will be the one we get. The simple reason for this is that I would guess a RO box would be time period 2, and the Inquisitor would be dead by then, therefore...
I believe the next box will be Rebels themed. To what extent, I cannot say; personally I would hope we only get a few of the Ghosts as allies, and would be very upset if we get any as heroes. But this expansion could give us both Imperials and Mercs. It would allow for all of the wave seven figure packs. And there would be enough content to warrant a big box.

