Can you imagine how they will RETROACTIVELY ruin Vader? I can. Wrong voice, wrong height or build or walk. Wrong personality...they are going to eff it up.
I am sure they will still get James Earl Jones to do the voice..he does it for REBELS, don't see why they wouldn't get him for this
and remember,this is a younger Vader then in EP 4, so he may be a bit more "energetic" in his actions as well as even more set in stone on the dark side path after his fight with Ashoka that we saw in REBELS. That is, a full realization that none of his old friends will come to him no matter how strong their previous bond was, they will not go dark as he did.
and i do agree with APE and anyone else who says this movie--and all movies--are about money and milking said cash from the SW cow
but it is also filling the "holes" in the SW's story that fans have longed to see told on screen
we do get tired of the Skywalkers and Solo's, R2D2 and C3PO. We know there is a hole set of other characters out there--millions are involved in the galactic war--we want to see their stories and roles in the over-all story.