I guess they could force Mara into BoBF and then have her relationship with Luke be offscreen; maybe he doesn't even know they have a kid and there is your sequel sequel trilogy? How many great scenes are we going to miss by them just not making that trilogy the movie? A whole planet that worships Darth Vader as a savior making the audience (and Leia) think that he had some redemptive qualities only to find out that he was using them as slaves the entire time? Brutal. Also, Luke willingly studying the Force with an unstable clone because there is no one left in the galaxy who can actually teach him. The EU did such a good job of trying to show Luke as someone who only knew the Force through mythology and old fanatics; it showed his inability to shepherd the Jedi back from extinction because he he was really only taught to use it as a weapon.