It seems that Nuke The Fridge started the rumour, saying that the added material will include:
Bane's origin plus a bit more screentime for Ra's Al Ghul which were omitted from the current theatrical cut of the movie.
I'm feeling pretty sceptical. I don't know why Nolan wouldn't have been allowed final cut for the theatrical release, nor do I expect he's changed his mind about what the film should contain in the last few months.
Also note that no previous Nolan has existed in multiple cuts, unless you count that novelty, detangled version of Memento.
Still, Nuke the Fridge were wise enough to buy that URL, and they have found the odd little bit of scoop over the years. I don't think they're having us on.
An official announcement for the Rises DVD and Blu-ray can't be too far away. Any extended cut would surely pass through ratings boards before long, too. I'll be keeping 'em peeled.