After recently announcing that Team Deathmatch would not be making the cut for Diablo III in its current form, Blizzard did mention that another aspect of player-versus-player, dueling, would move forward. Scheduled to arrive via patch 1.0.7, dueling will be accessible at a new in-game zone with up to four players supported, free-for-all style.
A few notes, as described by Blizzard's Wyatt Cheng: dying results in a respawn within the dueling zone; death isn't permanent (this includes Hardcore characters); and players won't take durability damage. "The game doesn't keep score and there are no objectives. We wanted dueling to be as simple and straightforward as possible, so we created a minimalist system -- we know that even without rewards and objectives, some players just want to beat each other up."
While dueling is one of the bigger additions to Diablo III in this patch, 1.0.7 also contains a number of tweaks to gameplay systems, like experience bonuses from Monster Power and a new gem tier. Additionally, Blizzard will be introducing Rare crafting recipes for some account-bound items.
Patch 1.0.7 Preview [Battle.net]