At his PAX Prime keynote panel today, Hideo Kojima confirmed that upcoming game Metal Gear Solid: Ground Zeroes will serve as a prologue to Metal Gear Solid 5. It stars Big Boss as a main character. Not Snake -- Big Boss.
Ground Zeroes is a current-gen game, running on the FOX Engine. It was shown on a PC, but Kojima says that the visuals are comparable to that of final PS3 visuals. He says that today's demo should closely resemble the PS3.
So, PS3 confirmed! Expect to see this game on at least PS3, if not Xbox 360 and PC.
Stay tuned to see gameplay.