According to the latest issue of the June / July French IG Magazine, the creator of Metal Gear Solid confirmed that Metal Gear Solid 5 is well underway.
Both quotes by Kojima:
“There will be a Metal Gear Solid 5 with the new FOX Engine, but what we’ve shown was not gameplay, or anything like tha,” said Kojima. “It was only a demo that we had developed internally and released because the lighting and interactions with the environment had fooled everyone.”
“About Metal Gear Solid 5, I can tell you two things. There will be much question of infiltration, espionage, and convincing people to give you “a favor” like in the last Metal Gear Solid. I liked the idea of social interactions in Deus Ex: Human Revolution, but we will see,” Kojima revealed.
I'm bummed out by more Solid Snake after saying that his story is over (see; my upsets if a future Half Life game starring Gordon Freeman after the next irritates me), but glad to see the DX influence turn full circle.