The Deku Tree returns in Breath of the Wild and its feet the legendary Master Sword rests. The Koroks are all over the forest as well and all of this raises more questions about the story of Breath of the Wild and where the game might take place in the timeline.
The quote from the Deku Tree in the newest trailer is interesting, because he implies that he has talked to Link before, but he has simply forgotten, what has happened hundred years ago. It might even be that Link left the Master Sword in the protection of the Deku Tree and now has returned to claim it again.
It might also be that the Deku Tree isn't referring to this new incarnation of Link, but to the Hero of Time or the Hero of Winds or the soul of the hero in general, which is reborn ever so often. We can't say for sure.
But in general this is a very curious setting. In the three timeline branches we've only seen the Deku Tree and the Koroks in the Wind Waker, which on first glance supports the idea of this game taking place after the Wind Waker, in a time where Hyrule has risen from the Great Sea again, probably long after Spirit Tracks. The Zora don't really fit in there, because they supposedly evolved into the Rito, but the new Zora in Breath of the Wild could be some oceanic subspecies.
On the other hand it's curious, how in the trailer we can see the Hyrule Castle Town from Twilight Princess getting destroyed by Guardians. But of course it could just be that a similar castle and town was built in the newer new Hyrule. But it's also curious, how the Master Sword pedestal still looks exactly like the one from A Link to the Past and A Link Between Worlds, just much older, and it's entirely possible that the Deku Tree grew in the other timeline branches as well. It could be that he was there in the same location all along, but you couldn't see it in A Link to the Past and A Link Between Worlds because of the cropped topdown view. Imagine that! This would certainly create an interesting mindfuck.
But overall I'm still a fan of the timeline merge theory that I've been advocating since E3. It's still the one "explain it all" wildcard that really would provide a restart for the franchise built on its entire past. But more about that later!