We’ve already seen some characters from the original Star Wars trilogy appear on Star Wars Rebels, but the idea that things could go in the other direction is a new wrinkle.
What happens in Star Wars Rebels can have a potential impact on the characters in the films, even if the events are unseen.
Simon Kinberg, producer of the Star Wars Rebels animated series, recently told Empire that similar crossovers could occur for his show, going in both directions.
The Star Wars expanded universe got absolutely massive with all the novels and comic books created, but it was mostly an entity unto itself.