It is a huge challenge to add gravitas to a story involving such a perfect and perfectly silly character. Probably better to go in the other direction (more Iron Man than Dark Knight) with Superman. They tried twice with Hulk, three times with Punisher--some comic book characters just don't lend themselves well to poignant storytelling.
Zack Snyder (Watchmen, 300, Dawn of the Dead) is now expected to direct with the script being written by Christopher Nolan and David Goyer (Batman Begins, The Dark Knight) both of whom will also produce. Pretty much an all-star team.