O lawd. I don't want to have to go over this again. D=
Metal Gear Solid 4 will NOT go to the 360. This is because in order for the 360 to get a perfect port of MGS4, it would need multiple discs due to the fact that the 360 uses DVD format and the PS3 uses Blu-ray. Although it's technically possible, the production costs to make multiple discs would be through the roof.
Also, Kojima enjoys working with the PS3, so most (if not, all) of his games would be PS3-exclusive. He's not a sellout, he actually enjoys his work. This also reduces the chance of any future Metal Gear games on the 360 to near-zero.
So you see, it's extremely unlikely that the 360 will ever get a Metal Gear game.