The Phantom Pain is a Metal Gear Solid game. That's beyond debate.
There are myriad reasons why - from the negative space on The Phantom Pain logo spelling 'Metal Gear Solid V', to the presence of Kyle Cooper, a Hollywood title sequence designer who worked on MGS2 and MGS3, wearing a Moby Dick Studio T-shirt at the VGA awards.
Official PlayStation Magazine, blogger DivineDiablo and NeoGAF's incredible investigation thread provide solid background to the theory of where The Phantom Pain fits into the MGS universe - and here are 21 more lesser debated, but significant, observations from trailer...
1. The Doctor is Kio Marv... or is he?
Visually, the doctor looks a fair bit like Kio Marv, the Czech scientist who invents Oilix from Metal Gear 2: Solid Snake. Marv dies during the Zanzibar Land Disturbance (outlined in MG2: Solid Snake) in 1999 - so this loosely fits with the anticipated early 70 to late 90s setting of MGS: Ground Zeroes / The Phantom Pain.
However, Marv isn't a medical doctor (he's a scientist) and - critically - speaks no English, only Czech and Slovak. It's possible that the central character (assumed to be Big Boss) is in a coma, and *imagines* he is speaking English, but this is tenuous.
Dr Madnar, a Russian robotics engineer, is less of a visual match, but makes (slightly) more sense. There's a rumour that Madnar performs emergency surgery on Big Boss somewhere during the MGS timeline, replacing his limbs and major organs - as mentioned in the MGS4 database, an official downloadable application for PS3. In the trailer's final words, a female voice says "V has come to" - in (what sounds like) a Russian accent.
2. The bandaged man isn't the burnt man from MGS Ground Zeroes in disguise
Speculation suggested the burnt man was hiding under the bandages, but when you see the bandaged man face on, he looks younger - and there's no visible scarring on the sides of the mouth. It's quite possible that he suffers the burning during the events of The Phantom Pain, since the chronology of events is hugely up for debate, but this is speculation.
3. The car crash takes place after the events of the trailer
In the car crash scene, the bandaged man is driving, while Big Boss sits in the passenger seat. Big Boss has a prosthetic arm, so it isn't the crash that causes him to lose the limb. The car is full of pills, tablets and pens (all hospital equipment), and the bandaged man is holding a clipboard (likely a patient roster).
It's unknown why he's taken it, and the text isn't clear enough to see if it's one of the clipboards visible elsewhere in the trailer. It's likely they're driving an ambulance and escaping the events of the trailer. It's unclear whether this is a *literal*, failed escape attempt, or Big Boss thwarted in his attempt to wake up by his own subconscious / his captor.
4. The car dashboard looks early 1970s
There are no digital readouts, and the speedometer is a giveaway - in the style of US classic cars like the 1970 Ford Torino. If you glimpse to the far left in the trailer's climatic scene, before Big Boss sees the flaming whale, you can glimpse the front end of an ambulance - likely the escape vehicle.
Earlier in the year, Kojima tweeted FoxEngine test images showing - what looks like - two texture-less 3D ambulance models. The ambulance resembles a 1972 Chevrolet Vanguard. The year is significant. 1972 is when the Les Enfants Terrible project takes place... while Big Boss is in a coma.
We couldn't find a picture of a Chevrolet Vanguard ambulance dashboard, but the picture of a 1972 Chevrolet Concourse Wagon above is very similar - note the speedometer.
Earlier in the same session, Kojima tweeted images of a car crash, with actors in mo-cap balls dangling upside down. This was followed by images of surgical instruments, and it seems fair to assume these are all related.