Random speculation:
The Ground Zeroes trailer features a disfigured man who seems to lead a group that can change and disguise their equipment (like removing the logo from the helicopter) quickly and easily. What if we're looking at the true face of Decoy Octopus? And now we've also got the theories running wild about Mantis being a part of the Phantom Pain trailer...
It's been speculated that Phantom Pain and Ground Zeroes are separate parts of the same game, so could we be looking at a story that revolves around the various FOXHOUND team members? Lets take it a step further
Remember the intro to MGS4? With the different television channels and ads for the various PMCs? What if MGSV is similar, and its actually a collection of five smaller games, each one telling the story of a member of FOXHOUND (with the exception of Revolver Ocelot) and playing in a different style? Ground Zeroes is the open world Metal Gear game, Phantom Pain as a sort of military horror game (something like F.E.A.R. but in the MGS style), and so on.
Its MGSV, not MGS5. That is to say
maybe its not the fifth game in the Metal Gear Solid series, but a game about five stories all related to Metal Gear Solid?
...I really want that game that exists in my head now.