well they just confirmed MGS5 is in the works:
Payton: Metal Gear Solid 5 - Prequel to Solid Snake [http://www.psbeyond.com/news/Payton-Metal-Gear-Solid-5-Prequel-to-Solid-Snake.666.html]
Payton: Metal Gear Solid 5 - Prequel to Solid Snake [http://www.psbeyond.com/news/Payton-Metal-Gear-Solid-5-Prequel-to-Solid-Snake.666.html]
and as a side note Konami has just trademarked the title MGS:Existence, most likely the expanded version of MGS 4 so not to much excitement there.When quizzed about MGS4 and the series' future, Payton explained: "There are some misunderstandings that this is the final Metal Gear game. But it's really the final chapter of the Solid Snake story. That's all."