Now many of you may want to react angrily upon reading the title of this post. However I hope that instead of reacting you listen to my reasoning.
I'll start out by saying that Nolan is a superb writer as well directer. And he certainly did a fantastic job of reigniting DC's cinematic hopes and dreams with writing and directing the incredible Dark Knight trilogy, one that I believe will go down as one of the greatest series of superhero movies ever made. He also was heavily involved in Man of Steel (serving as a producer of the movie as well as working with David S. Goyer on creating the story) DC's newest venture.
Now DC believes that it has a growing fanbase of movie goers and are willing to build their own cinematic universe to compete against their rival, Marvel's, impressive one. DC has already announced their next two projects, Man of Steel 2 (or whatever they're going to end up calling it (Steel Mangolias ~Loki)) and Justice League(woot!).
Now why shouldn't Mr. Nolan be involved in crafting DC's cinematic universe further? First lets look at what Nolan is. As a director, he likes it dark and realist-ish. Something that won't be welcome in a world full of space aliens , murmaids and rediculous heroes. As a writer, he prefers to keep things complicated. both of these things worked amazing with Batman, but Batman is one of a kind and is possibly the darkest most complex hero superhero ever created. However there really isn't another hero that can be crafted like that, definetly not if you are planning on making the atmosphere created in one superhero movie translate into other movies to form a cinematic universe. Added to that Nolan was asked to direct Justice League but declined. He knows that it's not right for him, and I know it's not right for DC, definetly if they want to prove that their superheroes are WAY better than the ones Marvel has. (Them's fightin' words. ~Loki)