For the most part I liked the PT due to their Greek Tragedy nature. I still don't understand all the rage over that.
This idea though is something to worry about, it not only makes RotJ pointless, it also destroys EU.
And nope, I'm pretty sure I won't be seeing these "Star Wars" films.
it doesn't ruin anything because
1. we don't know if the rumor is even true.
2. we don't know what in context. It could be in the form of flashbacks, holovids, or even visions.
3. It could also mean that Luke becomes Vader. Someone was talking about how Lucas wanted Luke to fall to the darkside in one of his early story treatments.