Newsarama offers a really good op-ed on why the next Batman film could - should be - called The Dark Knight Returns, and also why the Joker should come back. And be recast. Check it out. I think it may have persuaded me from my position that recasting the character would be difficult in the least. I don't know, however, that a literal translation of Frank Miller's Batman into Nolan's is possible or even feasible; that said, the article is good food for thought.
I've always thought Batman's story has to end. His success prevents it of course. Even if Nolan completes his trilogy, which is what we seem to be in for, Warner Brothers will want and rightfully so as many films as they can get. And they should make Batman films to their hearts content. This article suggests a great idea: allowing myriad artists take their own whacks at the character, in various films. Batman has proven his elasticity. But since we're talking about the first true, complete - possibly - Batman cinema story, it must end and let there be an ending.
Interesting article on the true cultural impact of the film. Of course, the inevitable backlash against it has already begun; anything this big cannot go unchallenged. This article makes good points about the film's flaws. I think it misses the boat on a few things - the direction is all over the place? - but it also links to some other discussions which again are good food for your brain. There is a lot of trying to make the film fit somewhere - superhero genre, crime genre, etc. Seems it either transcends all of them or just lands outside one or more of them, depending on who you talk to.