Apparently, the Star Wars magnate has been quietly buying the film rights to dead stars in order to "cast" them, using CG, in brand-new productions.
There's one big problem with this news of Lucas' zombie jamboree: It's coming from the British paper The Sun—which isn't quite the bastion of legitimacy one would hope. They're reporting that this news comes from Mel Smith, a U.K. comedian who also directed the Lucas-produced Radioland Murders back in 1994—and Smith being privy to Lucas' plans, 25 years later, might be possible, if unlikely.
Beyond that, the technology just isn't there yet. Avatar got away with photo-real characters because they weren't human. The blueness of it all made it easier for us to buy. But we can all too easily recognize when humans on the screen aren't human—especially when they're supposed to be giving an actual performance.
Of course, there will be progress and the tech will get better—and Lucas would know that, just as he'd know that we're a long way away from a film where Jimmy Stewart and Ryan Reynolds can convincingly compete for Marilyn Monroe's affections.