I just tried to find what would Lucas or a Disney executive do to make the true Vader come back (not someone pretending to be Vader)... And the best I found is this: try to find a way for Anakin's Force Ghost to take control of a new Vader's armor but working for the light side of the Force this time... Perfect Disney family movie: Son and father (and add the son of Luke too, for good mesure!) fighting together for the good of the galaxy ( and in a way they could even say that it is exactly what Vader wanted in ESB...!)

.... Ok, I go.