I am completely baffled as to where it could be.
The only thing I am pretty sure of is that it's not pre-OoT split. There's no way Hyrule could rise and fall into that state of great decay because of beast Ganon and then rise again in between SS and TMC, that's ludicrous.
However we need to pay attention to the details, specifically in some of the dialogue that was shown in all of the E3 floor footage and treehouse live footage. When Link wakes up, the voice tells him he is their light and must shine upon Hyrule "again". Then after he descends the resurrection tower, the old man asks him if he RECOGNIZES the voice he heard. When Link says no, the old man says it's a shame. The lines coupled with Link being resurrected from a 100 year sleep leads to the fact-- This is not a new Link.It has to be one we're familiar with, or at least one that has saved Hyrule before.
Though multiple aspects point to different timelines
ADULT- Champions shirt resembling Link's Crawfish shirt in WW, presence of Koroks, art style in general, bokoblin designs
CHILD- Presence of the Temple of Time, Wolf Link, Bridge of Hylia (?), Aonuma's previous Twilight Princess references
DOWNFALL- Hyrule state of decline, presence of the Old Man, intentional world similarities, location of the Master Sword (the scene in the trailer looks EXACTLY like the A Link to the Past master sword artwork setting)
Im thinking either Child or Downfall. Adult's Great flood complicates things because 1. Probably not New Hyrule, and 2. I find it hard to believe that the Great Sea disappeared. But the presence of Kooks does really trip me up.