If you look at the camera angles used in the Vader unmasking scene I imagine from a technical viewpoint it would be very easy to do this. Maybe Lucas had this idea all along and had Richard Marquand shoot it that way, and for some reason didn't follow through. On the subject of the quality of the CGI, many of the space battle scenes in 'A New Hope' still stand up and the Mos Eisle scenes can be given a 'fresh coat of CGI paint' especially the Jabba scene. Jedi is the one that needs the most work in my opinion. I'd have a CGI Rancor monster and maybe revisit the speeder-bike chase.
There are also a number of deleted scenes from Empire and Jedi which I think were good character moments that I'd put back in such as C3P0 tricking the Stormtroopers into encountering the Hoth monsters (with the previous scene establishing that the rebels have the creature also inserted). The longer scene with Luke and the others in the sick bay as well as the fate of Lando's computer aide Lobot. On Jedi the scene of the Imperial Officer who Vader encounters in the opening scene, raising objections during the battle to using the Death Star and the little battle Han & the rebels have when they first try to enter the shield generator.