Warner's wants another Superman film, they're just not sure how. But I don't think they'd be looking to The Dark Knight for inspiration. Superman Returns was as brooding as I ever thought I'd see Superman, and it didn't work. I think they'd look more to Iron Man, as it definitely had more of the lighter tone they should be going for in a Superman movie.
Perhaps TDK will give them a clue. It works because not because it's a great superhero story, but because it is a quintessential Batman
story. Just like Iron Man and Spider-man worked because they captured the essence and tone of those particular characters. Where they keep going wrong with Superman is in not trusting the simple core of the character. That's what made Superman: The Movie work. It is truly amazing to me that they can't get the most straight-forward superhero right... because he's straight-forward.