Because of how quiet they are being, I half suspect that the fourth season of Rebels will be of the renewed format, where they show's title changes and the cast potentially changes as the situation has changed. They move from being a group of Rebels to being the Rebel Alliance, and being taken seriously by some of the Imperials, leading into a two year run to Scarif and Yavin, with the potential for another year after that to see what the fallout of the Battle of Yavin is for the Rebellion. A third season of the renewed show would bookmark the release of Episode IX. After which the Animation department will be able to move in any direction.