I'm still confused as to were or how this fits into the plot. Here is what we know:
- Link wins the bird riding ceremony
- He and Zelda go flying around
- Ghirahim's tornado sucks up Zelda
- Zelda is saved by an unknown diety (accepting that the whale scene is a dream)
- Phi appears to Link and somhow saves him
- Link receives the Green tunic, and is seen with the green hilted Skyward Sword
- Link sets off to save Zelda
Link having the Hero's cloths would mean that he would have the Skyward Sword, and Link doesn't have the Hylian shield when he sets off for Hyrule. My only other theory is this:
- Link goes down to Hyrule, but must leave the Skyward Sword down below for it to be forged into the Master Sword
- The next time Link casualy returns to Skyloft, he finds that Ghirahim has invaded it
- Link must fight Ghirahim without the Skyward Sword, meaning he is left with his first junky sword
- Phi appears mid-battle and grants Link the Master Sword, wich he needs to defeat Ghirahim
This would mean that the depicted scene in the trailer is close to the end of the game, though I don't think that it will be the final boss battle.
Back when I heard that Skyloft's residents knew nothing about the world below, I imediatly thought that Skyloft was created to protect Link, Zelda, and most of Hyrule's population. I was mostly right about that theory, so I could be right about this one...