Bingowings said:
Lucas has repeatedly blinked at the idea of a Sith Lady in the film series.
One is reminded of how Marvel wanted to have the Empire build a second Death Star in the comics only to have the idea halted.
Similarly Zahn wanted the Sith to be the assassin race that would later be named Noghri.
In the original rough plans for a sequel trilogy Luke's sister (not Leia) was going to be the new focus leading to a show down with the Emperor at the end who would have by then replaced Vader as the chief villain.
Replace her with a new female Jedi and replace Palpatine with a fallen Leia and you have the bare bones of a workable story template that has some links to the OT but enough variation to be it's own thing.
Marvel did do that storyline. Perhaps a few details were changed, but it's essentially the same scenario.