And yeah, my silly belief that there is some kind of ceiling/sky world is based probably wrong but the way Zelda looks up at the end of trailer. Or that somehow the top of the sky wraps around into the caves.
I don’t know, Zelda games love their dual worlds and I just feel like there’s something more happening.
The current theory is this:
When the Malice shoots up into the sky the 'sky barrier' that seperates the skyworld from Hyrule breaks (this barrier also exists in Skyward Sword) causing the sky islands to descend into hyrule.
However, more interesting is the part at the end of the trailer where Zelda holds the Master Sword and the Zelda-like figure shooting yellow beams against the Moldugas is holding the same yellow tear as Zelda.
In the background behind the goat creature with the white Tear you can also see a Rito (who is not Tulin) holding the Champions Bow and the Green Tear (that Tulin has in the 'present'). All the artworks depict 7 tears = 7 sages.
While nearly all tears are accounted for in the trailer the red tear seems to have been stolen from a Goron as it is placed in Ganondorfs crown.
In other words... multiple characters hold the same tears and Zelda seems to be stuck in ancient garb with a pristine Master Sword in a version of Hyrule with no sky islands sitting on a pedestal that is later seen as a damaged sky island.
Considering Zelda is how Hylia keeps Demise / Ganon at bay it seems that her falling and not being in the present allows him to unlock his full strength (much like how it did in Skyward Sword).
These could be flashbacks or story events or... this game has two versions of Hyrule. One in the present during the 'Upheaval' and one in the past (presumably the Zonai age).
It could be just limited areas like Skyward Sword / The Wind Waker or a fully realized Past / Present like A Link to the Past / Ocarina of Time or something in between like Twilight Princess.
Right from the start the trailers of this game seem to have been edited out of order and link being able to rewind falling blocks and projectiles seems to indicate that some sort of manipulation of time and place is in play.