Luke turns evil
Don’t worry, this plot line never came true and Luke Skywalker remained as one of the main heroes in the film from start to finish. But there was talk that maybe it would be interesting if he turned into an evil sith lord later on in the franchise, what a twist that would have been.
Apparently, the writing team was thinking that it would be a good idea to have Luke kill his master Obi-Wan Kenobi and then turn into one of the main bad guys. We can not say that it was a terrible idea, we would like to watch that, but we personally prefer it when Luke Skywalker is just a force for good.