According to Hi-Rez Studios, Closed Beta 22 should bring the new Siege Mode.
Siege mode pits two teams against one another, each starting at the opposite end of the map from the other. The objective is deceptively simple: The first team to control four points wins the game. The game mode comes with a twist, however, in that capturing a point spawns a payload that then must be escorted to the enemy base. Failure to have a player along side stops movement.