I mean, there’s the land around Hyrule, and also the oceans as I was hinting in my comment. Yona is also apparently from another domain, which could perhaps a sea based one? They could expand the current Hyrule via the rivers and lakes as well as an even further restored Hyrule, perhaps expanding some of the towns and villages. As for story, I feel like they keep hinting at the Triforce without actually implementing it fully, so maybe that?
Deeper depths or higher sky also seems possible, though I don’t think they’d do that, as much as they feel prototypical to some degree. Seeing the original home of the Zonai would be cool though, if it’s still there extremely high up. Perhaps a proper dark world? I know the Depths are a pseudo-implementation of that, but even so.
There was a patent filed back in the Wii U days (September 2015) which also described a scroll wheel trigger. Looking back at it now, it seems very Switch-like, though people back then probably would have assumed it was a Wii U Gamepad 2. Maybe it was an old prototype for the Switch that they’ve converted into a Switch 2?
Here’s the patent, and here’s the linked PDF with some images.