He's been talking about doing even more "touch ups" on 4-6... adding the creatures from 1-3 so it looks like a more complete universe.
Article from around the time of the Attack of the Clones release:
If George Lucas had a penny for every time someone asked him when Episodes IV, V and VI were coming out on DVD he’d be… well, an even richer man. But, having repeatedly dashed hopes by insisting such a release will have to wait until the entire prequel trilogy is in the bag, Lucas has left fans worldwide clutching their solitary Phantom Menace disc and howling at the unfairness of it all.
Now, while we can’t do anything about the three year delay, we can reveal why the finished products will certainly be worth the agonizing wait. As distressed as the rest of you by the absence of Star Wars, The Empire Strikes Back and Return of The Jedi on DVD, Empire Online collared Producer Rick McCallum at the Attack of The Clones premiere to find out exactly what’s holding Lucas back.
"Three years is a long time, but that’s how long it takes," he said of the delayed transition. But what, you may ask, is taking up the time exactly? Well, never one to do things half-heartedly, Lucas isn’t happy with a DVD of the original edits, nor, it would seem, of the enhanced Special Editions. Having previously confessed to shooting a number of additional scenes for the original trilogy while filming Episode II and with many more to be lensed during the third prequel’s production, George has made it his mission to complete the story once and for all. And so, we asked, will this spanking new footage make its debut on the DVD releases when they finally arrive? "Absolutely," confided McCallum with a conspiratorial grin.