Konami's website confirms that a Metal Gear Solid game is in development for GameCube.
An administrator at Konami's website's official message boards has confirmed that recent rumors of a Metal Gear Solid title for GameCube are indeed true.
I might as be the first to tell you all. I can tell you that YES, just as Mr. Miyamoto stated, a metal gear game for the GC is in development, but honestly, that is all the info that is available.
This post is by "Administrator", a user with Administrator privileges and the first registered member of the message boards. It's pretty safe to say that this person works for Konami.
Clearly, there are no details on the game, nor do we have any idea whether this will be a remake or port of either existing Metal Gear Solid game, or an entirely new chapter.
We'll have more info on this announcement soon. Thanks to Ethan Pearson of Nintendophiles for the tip!