Having just read a topic speculating on/wishing for new species to be included, I got to thinking that I haven't seen a lot of speculation on other sourcebooks on this board. Ultimately, this kind of discussion doesn't often produce anything more than fun discussion, that's a worthy enough end. And who knows? Maybe the creators take community discussions into consideration when it comes to ideas and interest.
Now, for example, some say that a Tatooine sourcebook is inevitable. Personally, I'm more eager to see a Coruscant/Imperial Center sourcebook. It's an intricately multi-layered setting, literally, with both Imperial and underworld influences. Just think of how excited people were for the cancelled 1313 game.
And even more whimsical, I think it would be pretty interesting if the Age of Rebellion books went with something other than regions. Maybe battle sourcebooks with scenarios in which you can have your parties take part in Battles of Hoth or Endor. Or comprehensive guides to space and plantetary warfare or intelligence operations? Greater in-depth ship guides? Or a sourcebook specifically on creating Imperial PCs. How cool would that be?