I think the ending of The Dark Knight was implying that, with him on the run as a vigilante. It's a plot point that's been in development since Batman Begins .... that he's not a vigilante, that he's something more, yet now he is exactly what he didn't want to be. So unless Nolan reverses that cycle, I think a big part of the next film will be Bruce coming to terms that he is Batman indefinitely.
Oh, I think that was the major character development of TDK. Bruce accepting his dark destiny so to speak by taking on the murders of Harvey Dent. The whole character arc of TDK hinges on him wanting to give up being Batman to the hero-in-the-light, but events force him in the exact opposite direction.
I wouldn't be surprised if there wasn't some sort of Dark Knight Returns ending. An army of inspired Guardian Angels sort of thing. We could see a sort of descent into darkness as Bruce bitterly comes to terms with being forced to stay as Batman evolving into a more hopeful acceptance of his ability to inspire others to justice. No death, no unmaksing, no direct passing of the singular torch to a successor, but more a change from singular warrior to underground general.
One thing Nolan has been good at has been taking inspiration from existing material and mixing it with outside influences so it seems natural he'd look at things like DKR, Kingdom Come and Batman Beyond.