Which game will sell better... the next Kojima game or Metal Gear Solid 6?
Just my opinion, but his last good MGS game was 3. Review scores aside, I don't think he brought that perfection design effort to anything games past that and it was hard for a bunch of remakes and rereleases and HD versions to sway the masses once he finally decided to take his show multiplatform. His efforts on Xbox so far are Ground Zeroes which they put a half assed effort into, which is damn near a demo anyways and The Phantom Pain and him constantly rereleasing titles. The Phantom Pain could've planted a decent seed, but now he is back to being exclusive to PS again... I can only see a scenario in 7 years where that cycle starts again.
That is his works as a multiplatform guy with his biggest franchise; so it's not wonder that the majority of his fans are on PlayStation.
Honestly I think he was sick of making MGS games, he's said in the past he was going to move on and he ended up getting death threats for it. It's really hard to bring your A game when you don't feel the passion for the project/series anymore.