So what could this mean?

[Syncopathic]

http://www.konami.jp/kojima_pro/mgst/?ref=kjp_jp

A MGS4 port to the 360?
A new MGA game?

Discuss.

[Macawmoses]

I'm betting on the port to the 360, myself. Which isn't exactly unforseen.

[Nayrman]

I'm betting on the port to the 360, myself. Which isn't exactly unforseen.

too many problems to overcome. (graphics, game size, multiple references to the PS3, so on and so forth)

It's probably a new spinoff game.

[Triforceman22]

Kojima WAS hinting about MGS5....

maybe it's for the 360?

[Tupin]

Kojima WAS hinting about MGS5....

maybe it's for the 360?

He has a 360 dev kit in his office, he's doing something with the 360.

[Nayrman]

Kojima WAS hinting about MGS5....

maybe it's for the 360?

I doubt full blown MGS5 would be 360 exclusive (since the Xbox does HORRENDOUSLY bad in Japan), although just the announcement is possible.
I bet it's another spin-off/side story like Acid was for the PSP...

[Red]

I think there are a few possibilities.

A port of MGS4.
MGS5. (Not really, but still.)
A spin off.
Metal Gear Online.