i think ultimately the only mgs game that may never see a proper port elsewhere is mgs4
allegedly the codebase is quite chaotic due to struggles getting used to the ps3's architecture (and it shows, as quite a few areas are probably unpolished due to the sheer virtue of managing to get it to work at all), and i'm sure in the documentary from one of Metal Gear Saga DVDs you can see that caused some staff tension
i remember reading something about the problems developing mgs4 spurring the development of the fox engine, but i'm not 100% certain
i'm fairly sure red dead redemption didn't go to pc for similar reasons (fucked code, but not as a result of any specific console, we all know that game was hell for the developers for a number of reasons), any attempts at porting would be incredibly rough and could end up breaking a majority of the game, requiring a heavy overhaul that isn't really budgeted for when doing porting work
i wouldn't mind an mgs4 'do-over' where kojima or someone else reimagines a majority of the game though. outer haven would get snipped entirely if it were up to me, and act 3 would change location from prague to london, imagine how cool it'd be to have snake walking along london bridge at night with big ben and the houses of parliament as the surroundings (plus it'd be ripe for a reference to the introduction of james bond in dr no), but i digress