"No, Luke: *I* am your mother!" Problem solved. There's nothing fundamental about Vader / Anakin Skywalker being male that's paramount to the story. The important part was he/she gave birth to Luke and Leia, and passed on the Jedi powers (and savior stuff). He was basically androgynous in eps IV-VI. And the fact that he was male in the first three? Ehn. Starbuck and Boomer were recast as women. It was just a reboot.