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.
I think you're misinterpreting the statements some folks are making re: "The Dark Knight" or "Batman Begins" regarding how Superman would be done.
What these films demonstrated isn't that "dark and brooding" is the way to go. What they demonstrated is that staying as true as possible to the source-material, instead of trying to "reinvent" or "put my own spin on it" or whatever, is the way to go.
"Superman Returns" at once tried to honor, not Superman (the comic character) but Superman (the Reeves character) and yet to "update" it in ways that they'd NEVER do with the comic character. They "honored" stuff that's not central to the guy, and ripped out core elements of him and those around him.
As "cool" as the action sequences in S-R may have looked, the "Superman is a stalker ex-boyfriend" bit was utterly horrifying to me and ruined everything. The fact that the actor, or at least the way the part was written and the character was outfitted and dressed, was almost like a Goth/Emo version of Superman didn't help.
Go do a search for "World's Finest trailer." It's a fan-made thing, but it's got the best Batman and Superman casting I've ever seen (and I love Bale in the Nolan films, by the way... I just think that the guy in this is better!) The guy who did Clarke Kent in this little trailer IS Superman as I've always seen him in my mind's eye. And his Clark and Superman are just dissimilar enough that I can imagine people not figuring it out.
What needs to be done in the next Superman film is to treat it as a SERIOUS (no "camp") treatment. Treat this as the real world... but just put this fantastic character into it. The Salkind Superman did that to an extent... but it also had a heavy dose of campiness, with "Superman Returns" kept but layered on even more heavily.
Note: "No Camp" does NOT mean "dark and depressing." Humor doesn't have to involve self-mockery. Superman should be a bright, positive hopeful character... exactly the opposite of what Batman should be.