It will come out right after TF2 does.
Honestly, delaying and delaying and delaying projects like this is a really bad idea, and you would think that game makers would realize this after Daikatana. Daikatana was stalled for years and when it finally made it to the shelves, it was underwhelming compared to UT and Q3 which were out at the same time. If DNF comes out after Doom3 and HL2 are out, it will be just as doomed.