Jay Wilson posted the PvP Blog today. It explains the iterations and internal testing of Team Deathmatch Mode. The feature has been deemed not at par with the expected Blizzard-quality standards. Again, the Diablo III Team is scratching Team Deathmatch, and starting anew — back to the drawing board.
Dueling, however, will be available in Patch 1.0.7 sometime during early 2013. There will be a Dueling Blog update before the patch goes live.
Is all lost for Team Deathmatch? There is a possibility it might return at some extent. No promises there. What the Diablo III Team is considering now is to offer Team gameplay with PvE elements and a reward system behind it.