The director and creator of the Metal Gear Solid series, Hideo Kojima, has been quoted in regards to Metal Gear Solid 5, where he has said:
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 'favour' like in the last Metal Gear Solid. I liked the idea of social interactions in Deus Ex: Human Revolution, but we will see. And if I say more, the female ninja public relations officer, who is behind the door, I will be carved up into pieces. So it's better that we meet again when the time comes to talk about Metal Gear Solid 5.
Metal Gear Solid 5 should also sport the new FOX Engine, and I'm personally pegging it to be released on whatever Sony's next-gen console materializes as, the PlayStation 4 most likely.