Hopefully not the ghost of Hayden as the villain.
But seriously i don't know. What if Luke is the bad guy, but that would be totally unoriginal like Dark Empire. And be too derivative of how Kasdan wanted Jedi to end.
Seriously watching Hamill cackle like Palpatine would be like a live action Joker.
Not something we want i would imagine though it might be entertaining for a second or two.