Yes, its a pending type of thing. I agree that if MGS4 doesnt hit 1,000,000 within two weeks the 360 port would be inevitable regardless of whether or not it is planned as of now.
However, I doubt that will happen. Its Sony's top gun for the year. It will get advertised like hell, in every region. If it sells well, that will also serve as a good argument for Final Fantasy to remain exclusive.