A few days ago, Hideo Kojima attended the opening of the new Kojima Productions studio on Los Angeles. This department will be creating the online portion of Metal Gear Solid V, the new Metal Gear Online. No one has seen it so far – except for Kojima of course.
In another tweet Kojima mentioned the staff of the earlier MGO games is still involved in the development of the game.
MGO’s been developed @ LA studio by our elite staffs. KoreP & original MGO dev staffs check frequently.
When MGO will be revealed to the public has not been announced, but Metal Gear Solid V will be at the Tokyo Game Show later this month.
Source: Hideo Kojima Twitter