The group that created Rez has announced that DLC will not happen.
Sorry, no source, I heard it from the 1-up show.
They did say that they plan on doing more work with Rez.
All of their work, if they decide to work, will go towards Rez 2. And they plan on releasing it as a DLC through 360 and PS3.
Retail complete: Halo 3 (pre-update) | TMNT | Avatar | Bioshock | CSI | Oblivion | Madden 06 | NBA 2K6 | NHL 2K6 | Call of Duty 4 | Sonic's UGC | Resident Evil 5 (pre-update) | Fable II | Left 4 Dead | Lost Via Domus | Halo 3 ODST | Assassin's Creed 2
XBLA complete: Arkadian Warriors | Pac-Man CE | Golden Axe | Aegis Wing | SoulCalibur | Fable II Pub Games | Meteos Wars | Dash of Destruction | The Dishwasher | Rez HD | Uno