I don't have any doubt that the Phantom Pain trailer we saw was nothing but a MGS trailer. I don't think anything in it is a literal clue to what any game will be like, though. Volgin is already dead, so is The Boss; all of this screams Big Boss's 'dream'. MGS3 had a vampire-themed, black and white, hack 'n' slash dream sequence... I think this is probably the closest thing this trailer references in what will be 'Metal Gear Solid Ground Zeroes'. Taking the hints so literally as a separate game seems bullheaded.
IMO, Phantom Pain is related to what we know as MGS:GZ, and not a third concurrently developed Metal Gear. I'm sure MGS5 is a thing, but I don't think anything we saw was related to it.