If you visit the Japanese Konami site right now, you’ll see a simple teaser that implies that the next Metal Gear game coming will land on the Xbox 360. Below is a screenshot of the site.
While it’s not definite proof or anything, it really looks like the Xbox 360 power button there. With Microsoft wrapping up a lot of nice exclusives and big 3rd party releases in Japan lately, it’s not too big of a stretch to see Konami putting the next game on the 360. However, it’s also possible that this could just mean a port of Metal Gear Solid 4 to the 360. Either way, it’s big news for Microsoft if it pans out.
Link to the Konami site: http://www.konami.jp/kojima_pro/mgst/?ref=kjp_jp