Was there a time frame for when this secret would be unveiled?  I'd somehow gotten the idea that we'd get the news at GDC.  Did anyone but Nintendo announce any shit this year, or what?

I think its next MGS after Kojima Keynote.

Isn't there talk of a Kingdom Hearts announcement in a few days? Could be KH 3.

Halo 4

It's going to be MGS5.

Kojima basically announced it at GDC today.

Assuming the rumored announcement is true, yes. However every single Kingdom Hearts announcment since the first has occured at Tokyo Game Show, so it's fairly unlikely that Kingdom Hearts III of all games would deviate so radically from this. Furthermore, there would be no point to revealing it so early. Square Enix still has three Kingdom Hearts games in development to get out the door first and the Kingdom Hearts team is currently completely occupied by both Final Fantasy Versus XIII and Final Fantasy XIII. Development hasn't even begun, so an announcement would serve no purpose.

*edit* lol, oops. Didn't see the dates. Sorry for the bump.