While you don't actually see it on the movie screen, maybe they tweak things so that while Obi Wan is watching over Luke on Tatooine, Ahsoka goes to Alderran to be Leia's guardian angel.
That job has already been filled
I do think it's a cool idea though. And of course the TV show trumps any novels, comics, or games, so it could still happen.
Not to mention young reader novels. Fess Ilee/Ferus Olin can move over.
At this point, I think the question is: What hasn't
been thought of already in the EU?