Dark Sun!
Please, please please.
I've been waiting for 12 years for the re-emergence of official Dark Sun products updated for the new rules of the day. Dark Sun was the best campaign setting ever published, but it was ahead of its time. The majority of the gamer fanbase wasn't ready for that kind of story aesthetic and theme back in the early nineties, but it seems clear to me that we are now.
Dark Sun for 4th edition would be perfect, and amazing. Since Bill Slavicsek is the top dog of the whole department which makes D&D, and he was the lead designer of the revised Dark Sun setting (and heck, his first project ever for TSR was a Dark Sun supplement), maybe he'll steer the ship in the right direction for us.
Let Athas rise again!