I find the trailer pretty unsettling to be honest.
Watching the VGA's it didn't really phase me. At 3 AM in the morning it really is unsettling and eerie. Bigboss having a coma nightmare like this makes sense, and a lot of things in the trailer allude to his life.
- Volgin covered in flames, not dead from the last time they met. Glowing red eyes.
- Flame Unicorn representing The Boss's horse, a reminder of their relationship
- Raikov/Eva/The Boss covered in flame
- The whale launching and destroying the helicopter could allude to Bigboss's experience with fighting and seeing the Shagohod.
So this is a coma nightmare, which is effecting Bigboss's emotions and the player's emotions also. The fire and flame motif actually makes sense. The nightmare shown takes place after Metal Gear 2, the two phantoms tagline could mean you play as both Bigboss and Solid Snake. What you do and how you play as Bigboss will effect and change how you play as Solid Snake.
The first act of MGS V will be Ground Zeroes, you play as Bigboss and build up Outer Heaven. The second act will have the player playing as Solid Snake and infiltrating and destroying what Bigboss/the player previously built. The third and final act will be Solid Snake infiltrating Zanzibar Land, this time the player will have no knowledge or previous experience with what Bigboss has done.
The finale being Solid Snake burning Bigboss would lead to what's shown in The Phantom Pain trailer, The Phantom Pain is actually just the epilogue of the game, the player plays as Bigboss when he's in his coma. Kojima potentially showed us the last moments of the game without actually spoiling anything.
