Well, I think it's fairly safe to say SOMEBODY IS GETTING KILLED OFF in VII, hands down.
Theory 1: It's going to be Luke because Qui-Gon died in I, then Obi-Wan died in IV, and so a Jedi must die in VII for the "literary theme" to continue.
Theory 2: Han Solo, mainly because of Harrison Ford, lol. We all know why.
I think Luke might definitely take on a mentor type role in the films. Critical to development, but not the main guy swinging the saber.
It's really hard coming to terms with any theory because the Expanded Universe content has gone to shite.