Hideo Kojima just cannot quit the Metal Gear franchise. Yes, he's said he's quitting about a billion-million times, but if that were true, he wouldn't be already working on concepts for Metal Gear Solid 5 now, would he?
I have three concepts for MGS5 already. What would be ideal for me with MGS5, though, is that we don't do those. If the team picks one of those concepts, I have to get involved again, which I don't want to do. There are already so many good ideas from the staff, so if we select one of those, that would be really good. At that point I could really rely on them and take the step back to be the producer, which is the ideal situation, I think.
Whatevs. We all know what's really going to happen! Those three concepts will be cobbled together to form one large, unwieldy concept, and you'll carry on as producer, complaining the whole time that MGS5 will be your last MGS game.
Hideo Kojima MGS4 Afterthoughts [1UP]