In an interview with IGN, Kojima explained the reasoning behind the decision to go with Raiden despite his initial desire to have a game starring Frank Jaegar.
It was actually not my idea, it was my staff in Kojima Productions that insisted on Raiden, and I respected their idea. I wanted to really focus on production than development, and they wanted to come up with a really cool hack-and-slash title with some Katana action and Raiden in it, and I thought ‘okay, that’s fine, I respect that’.
But in my personal opinion, I wanted to go for Frank Jaegar or Gray Fox. But if we had gone with that, I would have had to write the script and then be really committed to creating the game. I want to pass game development to the younger generation in my team, and have been trying to do so for quite some time.
I don't know about you, but I really hope that this doesn't rule out the possibility that we'll one day see a Metal Gear Solid title centered around the tragic tale of Gray Fox. Are you glad that we're getting to play as Raiden in Metal Gear Rising: Revengeance or would you have rather seen a game starring Gray Fox as well? Let us know in the comments below.