Hideo Kojima was hanging around Twitter after his press conference today to talk a little bit more about Metal Gear Rising: Revengeance and the future of the franchise. Kojima clarified that Metal Gear Rising was always intended to be a spin-off series and intimated that their original vision is not too far off from where Platinum Games is now taking it.
More importantly, Kojima asked that fans who want an "authentic stealth MGS" to patiently wait for "the sequel coming in the future." So, it's not exactly confirmation of Metal Gear Solid 5 per se, but it is a confirmation of a new Metal Gear Solid title. Take that as you will.