I'm very surprised Nintendo is showing us this much cinematic footage, especially from such late point in the game. Up until now everything has been from the beginning of the game, the exceptions being very brief clips of temple gameplay and item menus. Of course, who knows how far along this footage actually is; it is a very long game after all. Judging by Link's shield, it can't be that far in, but it is the furthest we've seen.
The shots in this trailer are gorgeous, but I do think this is a bit much. I was hoping they would hold back on the story points until November. However, we have seen this part of the game before. This is the very climatic sequence, which we have been lead to assume was Ghirahim attacking Skyloft.
It is quite clear, by the gorge and the background mountains, that this structure is earth-bound. Zelda is in her white dress already, but she isn't being sacrificed or anything, which makes me wonder what prompts her to initially wear it. She's with her Sheikah body-guard, and Link has finally caught up with her. However, they are ambushed by Ghirahim, who we know has been tailing Link.
Zelda, being her quick-thinking self, uses magic to send the lyre Link's way. After the Sheikah's barrier fails, Link somehow gets past Ghirahim's barrier and fights him off.
The next few sequences show Fi dancing to the music of the lyre. It appears that some sort of portal is being made between the structure below and Skyloft. The two structures were probably originally connected before the Goddess brought half of it to the heavens, which would explain the gorge and the Hylian crest:
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wow just wow amazing