If we do see a MGS4 port. There are two things you need to know.
I am not saying there WONT be. But the likeliness is 20% still.
Secondly. If we do see a port, it will be ATLEAST a year from the day its released on PS3
Understand. Hideo Kojima took a year to port mgs2 onto xbox, and that turned out shit, this is because, like most games should, they are designed for a single console, and thus using all of its strengths.
So the bottom line is. If there is a port, we would see it a hell of a lot later, and it will be, not might, will be a weaker version then the PS3 version.