A few seconds of new footage for Ground Zeroes in this video.
So I guess Mother Base is, at least to some degree, playable, based on the footage.
It's already been confirmed to be all cutscene. Besides, how the hell would people think that's gameplay when he's shooting dudes with that camera angle? Having it pointed down and on an angle would make it hard to shoot dudes.
I am a dedicated member of the "Walter Sullivan Is Bad-Ass" group!!! I am the true originator of the Cookie Demon theory on the SH2 and 3 boards.