Update : More info has been added. Go here!
In the latest Kojima's interview with VG247, the father of Metal Gear Series reveals the Ground Zeroes will be his most mature game. It will tackle many taboos and he is concerned it may not sell as well for that reason. In the current game state, he admitted it may not receive a release day because of the maturity of the game.
“I may make more spin-offs, possibly with The Boss, which is something I personally want to do. But it’s not something I will make a habit of.”At last, Kojima wants Metal Gear Rising: Revengeance 2 to happen, but it has to be Platinum Games who develops.
“No one else could did it,”Source : VG247