Dunno what you've been reading, but one of the highest ranking people over at WB just said in an interview that everything is up to Nolan, they're waiting for Nolan, and implied quite heavily that Nolan is their god at the moment and he's in total command of anything and everything for the future. Which doesn't surprise my one iota, as the man just delivered them a $1 billion dollar box office bank note that's gotten more critical and fan acclaim than any other film this year, and may actually be the first 'comic book film' to recieve an Oscar nomination for acting as well as a potential long-shot at other significant categories.
In other words, right now, Nolan could take a dump on the desks of every WB board member, and he'd still be kneeled down before and sucked bone dry by every such board member. He's their golden goose, and he's got the reigns, the leash, the whip, and the ball-gag.
Nothing will occur with Batman until Nolan says so. Period. When and if he says, "OK, I'm not doing another one," and they give up on any hopes of bribes or pursaision to have him change his mind, then, and only then, will you maybe get to the point where the WB board of execs says, "OK, so, who else?" -- until that point, which I estimate is at least 4 to 5 years away, any speculation on who might 'take over' for Nolan is... assanine. To be honest.
In the end, I think Nolan will do the third film though. The reasons being...
5) He wants to finish the story he's set out to tell, and needs one more film to do it.
4) If he doesn't, he knows he'll always look back and wonder "What if?"
3) He has the best hope of any director to ever live of breaking the renowned trilogy curse, and actually making a superior successful third film.
2) He would have unimaginable power in making a third film, creatively, financially, so on and so forth. (I seriously think Nolan could kill off Batman and get away with it, he's got that much power with WB and DC right now.)
1) It's the ultimate challenge he's likely to ever know, and he strikes me as a man who can not pass such up. It's why he did TDK, after all. It was the ultimate challenge to him, at the time.