The xbox getting MGS2 isnt anything to go by, it was an experiment by Konami, they ported their most popular (non football) game and it failed to sell very well at all, removing much chance of any other future ports of Konami exclusives to the format.
Things are a little different now, since the 360 has twice as much of the market than sony does at the moment, but i dont think that will be enough to sway Konami into putting resources into porting another MGS game to a MS console.
Konami 'owe' alot of their success over the last 10 years to the playstation brand and unless the xbox stays with the same % of the market over sony, i cant see thier loyalties drastically changing.







