[Edit]
POST HOSPITAL STREAM IS UP
So here's some brief examinations of the hints dropped in previous trailers.
Kojima's Elegia trailer
+The obvious language theme ties in with the parasites and Skullface's plan
+The scene at the beginning is BB killing everyone at MB
+Les Enfant Terrible being talked about with Eli basically confirms he's Liquid, not sure WTF there are two Liquids though
2015 Gamescom
+The scene with Kaz and Snake pointing a gun to someone on the ground could be when they abandon Skullface to die.
Launch trailer
+The final boss battle is basically confirmed with Mantis controlling the Metal Gear
E3 2014 trailer
+Near the end of the trailer, three guys are restraining BB. However, they don't really say anything and are strangely silent. BB also shoots some guy just wandering around. This is probably also the MB massacre and the soldiers can't talk due to the parasite.
E3 2013 trailer
+Eli is dubbed "A youth who curses his fate." Obviously a hint towards him being Liquid and his fate being succeeding Big Boss and/or being a soldier for the Patriots.
+Ocelot is dubbed "A rival living a lie." Suits Ocelot because he's on everyone and no one's side all at once, but it could also tie into him knowing the ruse about Venom Snake not really being Big Boss.
+This is the first time we hear Ocelot talk about Big Boss being a legendary soldier and he says "Let the legend come back to life." Legends are of course stories that may not be factual at all, which ties in well with Venom Snake not being Big Boss (who receives credit for everything done in the game i.e. growing his legend).
Garbage trailer
+The much-talked about scene at the beginning where you are apparently seeing through the eyes of someone who is not Kaz or Boss was basically the first big hint that Venom Snake may not be BB.
+It also seems very little has changed from the hospital scene in this trailer and what we saw in the streams. Volgin is a bit more flammable in the stream version I suppose.