I just can't imagine Carrie Fisher playing the main villain... it would be laughable. I think her role in the film should be minimal.

Bingowings said:

Vader effectively reduced the Jedi down to the same numbers as the Sith (a master and an apprentice).

This left Luke and Leia (a master and an apprentice).

The force sensitives are born randomly across the galaxy so there is a plenty of other choices for villains. And why would the main villain even have to be force sensitive?

I don't think the trilogy should have one main villain. I think there should be more (imperial officers, crime lords etc.).