Our friend at JediNews have a source saying:
Ian McDiarmid is set to return to the galaxy far, far away for a part in Episode VII.
The specifics of the role are unclear, but it seems likely that McDiarmid will be returning to his signature role of Palpatine. Whether as the original or a clone of, we are yet to discern.
Could the Emperor be returning? Could he be a Clone? Could McDiarmid be playing the role as a flashback?
SO MANY QUESTIONS!
Just remember, all of this is just a rumor until Lucasfilm confirms it.