While there is a Metal Gear game coming out in Revengeance, that's not a sequel to Guns of the Patriots. But, Hideo Kojima confirms in a magazine
there will be a Metal Gear Solid 5
It seems Snake's tale is not done yet even though Kojima wanted to kill him off in four. I think it would've been a fitting end to the him if he did, but it seems we're going to get another Solid Snake story using the new Fox Engine to power the game
Kojima wants to add some of the social interactions like those seen in Deus Ex: Human Revolution into the game. Not much else was said, but I'm sure we'll be getting some teaser website or countdown when the time comes for Kojima to talk about the next Metal Gear Solid game.