I've never completed Majora's Mask. Can't provide any insight regarding this speculation, but I really don't care either way. I'm so hyped. I really hope we get to traverse beneath Hyrule and through caverns and secret passageways. I'm very curious about Zelda's involvement in the game. A co-op Zelda experience would be amazing!
The only part that's speculation is the precise identity of the body. The face logos we see throughout the video are, without a doubt, connected very strongly to Majora.
This pic is, of course, not from Majora's Mask, but the design is true to the game and shows crisply and clearly the detail. The design in the game is unmistakably reminiscent.
It may not be directly Majora-related - since it is slightly different in shape - but if it's not, it's at least tied to a cult of sorcerers or something that Majora was involved with. The creepy music, the atmosphere, and the hair on the corpse all are directly referencing Majora's Mask too, though. That teaser is chock full of clues that prove they're building off of Majora's Mask for this.
To what degree, though, will remain to be a mystery at least until next spring or summer, I think.
I do know one thing - I'm going to be digging out my 3DS and replaying MM3D before this comes out!