We know that Kojima is a tricky guy…
"The conclusion we reached is that Hideo Kojima may be thinking to give the fans a new edition of Metal Gear Solid 4, called Existence. As it did with MGS2: Substance and MGS3: Subsistence, Existence is probably a new edition of MGS4, with many extras and new gameplay modes, and the DLC is stated as a cost effective means to prolong the life of games, so it also may also be available for owners of MGS4 as downloadable content, so that they will enjoy this new experience."
