Now, the smartass answer would be to say "I wouldn't," but the ending is so vague enough that it's certainly possible with the right creative approach. The comicbook fan in me wants to see John Blake in the Jason Todd storyline where he becomes Red Hood, and obviously Dick Grayson as one of the orphans Wayne Manor has taken in. The tricky part, of course, is bringing Bruce Wayne back from the "dead," but it's been done before (Batman Begins). The even more difficult part is justifying him becoming Batman again after all the character development he went through in TDKR, especially with Alfred. It's tough, but not impossible.