It's time, as the self claimed biggest MGS nerd here, to do a The Phantom Pains (Henceforth PP and Ground Zeroes shall be GZ) trailer analysis.
"From FOX two phantoms were born"
The protagonist is clearly Big Boss. Don't go throwing Liquid's or shit like that at me. Liquid lacks the rugged brown mullet/beard combo and he died from FOXDIE 9which is essentially nanobots eating you from the inside).
"But, wait" you cry in anguished tones! "Surely that could be Solid Snake or even a young Solidius!" Ahhhh, you may be on to something, except the PP protagonist has a suspiciously similar scar on his cheek to Big Boss.
Another link to Big Boss is the presence of of white petals, used in Peace Walker to remind BB of his final battle with The Boss.
Now Big Boss is sneaking around with Bandage man. But who is Bandage man? Is he Frank Jaeger? Hush? Or is he the burnt villain form GZ?
The region of his wounds could suggest so, and the burnt man does seem to have some history with Big Boss. However another explanation for the burnt man is this fellow:
Who bears a striking resemblance to this fellow:
The highlights and the pants being the greatest points of comparison.
"Now just you hang on there, Deimos!" You exclaim, "Big Boss, if it is even he, is missing an arm and the bandage is covering his right eye!"
Very true, and there isn't a great answer for that yet. Big Boss is missing his right eye, Solid and Solidius cover their left, so this matches. Although who's to say Big Boss doesn't have a prosthetic limb? We know advanced replacements exist, even at that period, via Galvez.
However, I feeling that the events depicted in this trailer take the form of a corrupted flashback/dream sequence brought on by the mysterious floating figure seen at certain points. Namely here:
And in floating mode, here:
Could it be Kid Psycho Mantis? Note the very Sorrow like raincoat. Both characters known for mindfucking Snakes and this would explain "wrong" details as well as flaming horses and whales (Moby Dick, get it?). Psycho Mantis is also later recruited into Foxhound, which is originally led by Big Boss.
In the image of floating figure, the soldiers gear seems very reminiscent of the GZ troops:
But what's this? You still don't believe this is a MGS game? You think Moby Dick Studios is a new studio who managed to get Kojima's exclusive FOX engine?
Well by now everyone knows MDS CEO is Joakim Mogren, AKA Kojima mOGREn. Also IGN and G4tv writer Alex Ruben spotted some things at VGA's:
As well as this:
The person on the right is Kyle Cooper, mostly known for his work on the MGS series.
And then of course there's this:
But I still like to think this is very much Ground Zeroes, as the links to that are strongest and MGS5 is reportedly not past writing stage according to Kojima. Also why would you advertise for the game coming out after the game set before it isn't even out yet? That would be poor marketing.