I honestly don't think it'll ever happen. There's some money to be made in the move, sure, but Disney isn't primarily focused on the older generation of Star Wars fans; they're dedicated to creating a NEW generation of Star Wars fans. I don't think we'll see any revisits or re-releases of the prequels or original trilogy, as Disney wasn't involved in their handling and distribution. I think they'll want to keep them slightly separate, as if to say "This is what Star Wars was, and this is what it is now."
Based on Disney's recent releases, in about 50 years or so they'll remake the entire series (up to the current point, at least), but it'll all be one movie, told from Vader's point of view. It'll turn out he was a good guy all along, who LET Luke blow up the Death Star because he didn't want the Empire to kill millions of people, and he actually MEANT IT at the end of Empire when he wanted Luke to help him overthrow the Emperor.
HE JUST WANTED TO GET TO KNOW HIS SON, OKAY?
The prequels aren't even THAT bad, honestly. I mean, yeah. Midichlorians? Wtf. And Jar Jar needs to be hung from the nearest tree post haste.
I ain't even mad about midichlorians. It's an allowable (if somewhat hazily thought out) explanation of how Force sensitivity works. Though I long ago decided to think of them not as "what makes up the Force" but "what enables you to manipulate the Force", so my view may be somewhat skewed.
As for Jar Jar... re-watching the prequels last weekend only served to remind me that Jar Jar is actually a
necessary character. Jar Jar is a baffoon because that's what his place in the story called for; someone (with a good heart, mind you) who would be easily swayed by Palpatine's schemes into handing the keys to the Republic to the Sith, without even realizing it. It was Jar Jar who moved to give Palps the Emergency Powers that allowed him to eventually become Emperor, after all. So, in that light, Jar Jar, while still annoying, is at least forgivable (for his inclusion, if not his characterization).
And some of the script writers for those movies should have never been allowed near a script to begin with, as I'm pretty sure I could have done a far better job.. when I was 13. (which was how old i was when episode 1 came out.)
AHEMGEORGELUCASAHEM (The man can direct like no one's business, and he's got a great imagination for coming up with stories... but his writing, especially the dialog, is stiffer than C3PO's elbows.)