During his session at the European Gaming Expo, Kojima hinted at the possibility of a new Metal Gear Online title being developed at the Kojima Productions Los Angeles studios. Note that Kojima did not specify whether Metal Gear Online was a part of Ground Zero or a separate game entirely.
Metal Gear Online was originally the online multiplayer component of Metal Gear Solid 4: Guns of the Patriots. However, besides its popularity in Japan, the mode didn’t achieve much success in the West. Original Metal Gear Online’s servers were shut down in June 2012.
We will have more information as it becomes available.