I've been staring at that Next Metal Gear Image for probably hours I've come to several conslusions:

1. The next Metal Gear is NOT a new game
2. The next Metal Gear is coming to Xbox 360
3. There are actually 2 next Metal Gears
4. One is a Xbox Live Arcade Remake of Metal Gear Ac!d
5. One of the other Metal Gear Solids are being remade/ported for 360

It is possible that the Metal Gear Solid title is a Xbox Originals version of Metal Gear Solid 2: Substance but that would be a tad disappointing especially with the insane demand for MGS4 on 360. Anyways that's just my guesses and yeah nothing is official until Konami announce it but the five things I listed make the most sense to me. Of course they will probably go and announce a new Metal Gear for iPhone or some crap like that.