A new play mode has been confirmed for Starcraft II and is likely to be included in Legacy of the Void.
This new mode, called Archon Mode, allows two players to control a single army. I see this being helpful when trying to teach new players how Starcraft works. Full details will likely come later today during the Starcraft II What’s Next panel at 4:45 PT.
I speculate that the 2v2 exhibition matches tomorrow will be using this new play mode.