Via an exclusive interview with Gamepro , Hideo Kojima mentions he has his eye on 360 development, though of course there's no confirmation about whether it would be the Metal Gear franchise or a new IP. (Frankly I would be more enthusiastic about the latter, but that would be up to him.)
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GP: Is MGS4 still planned as an exclusive PS3 game? Do you have any interest in Xbox 360 development?
Kojima: Well, yes, I do have strong interest in creating something for the Xbox 360. In the US and Europe, it is selling, and I think it will sell a lot this year as well. I'm a fan of Gears of War as well, it's very interesting.
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GP: If you ever made an Xbox 360, would you find it difficult to work with because it uses a standard DVD?
Kojima: It's not necessarily challenging or difficult, it's just a matter of how we do it. It might be a couple of discs, or possibly a new form of dual-layer.
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GP: Is MGS4 still planned as an exclusive PS3 game? Do you have any interest in Xbox 360 development?
Kojima: Well, yes, I do have strong interest in creating something for the Xbox 360. In the US and Europe, it is selling, and I think it will sell a lot this year as well. I'm a fan of Gears of War as well, it's very interesting.
...
GP: If you ever made an Xbox 360, would you find it difficult to work with because it uses a standard DVD?
Kojima: It's not necessarily challenging or difficult, it's just a matter of how we do it. It might be a couple of discs, or possibly a new form of dual-layer.