I only know of one movie that went back to the original effects and scanned higher than 4k Star Trek the Motion Picture.

I suppose like there they could scan the Vistavision shots at 6k. It just seems like something Lucasfilm wouldn’t do when most of the special edition is locked to 2k or lower res anyway depending on the shot. In theory they could redo the original cuts in 4k or higher but we are talking about matte printers and optical composited visuals its not my level of expertise, the guys you’d have to ask are John Dykstra or Dennis Muren if it would be possible.