According to an interview held with French gaming magazine IG Magazine, Kojima has confirmed there will be a Metal Gear Solid 5.
The game will apparently run on the FOX engine and will once again feature much infiltration and espionage. It will also pick up on the concept introduced in MGS4, where you could convince people to do you a favor (he probably refers to the fact that you could help the rebels and exchange items with them). Kojima also mentioned he likes the idea of social interactions in Deus Ex, but he’s not saying it will necessarily be in MGS5.
In response to a question asking how he feels about Metal Gear Rising: Revengeance, Kojima responded that this was never ‘Metal Gear Solid’, but rather a spin-off that tries to do something new
Lastly, Kojima also implied the game will feature Solid Snake as a protagonist. He also said that despite wanting to kill him in MGS4, the studio is not yet done with Solid Snake.
Speculation: The artwork here is of Big Boss. But they are talking about Solid Snake. So maybe in MGS5 they may meet again. Who knows.