doubleofive said:

You can replace fuzzy shots of David Prowse from a distance, but RotS proved NO ONE can take his place.

Actually ROTS only proved that Hayden couldn't act his way out of a wet paper bag (as Anakin OR as Vader)

If there WERE work being done to fix the matte-ness of Vader's suit in the opening of ANH (and I'm not saying there is) then my guess would be that, in order to preserve the iconic acting job done by Prowse, a new Vader would be shot going through the movements and only PARTS of the costume would be superimposed over the film as it is now (specifically the helmet shroud)