I think Breath of the Wild/Zelda in general, it’s hard to say what route they would take with a playable character. I personally don’t think any of the ATs would be upgraded, especially when the focus is on BOTW right now.
With BOTW, however, we already have a stage and music from it. Given the fact that it’s the same world, we’d be getting another stage from the same “world” of BOTW, which...I personally don’t know what to make of it. The Great Plateau was the biggest part of BOTW, and it’s showcased in the Tower stage.The stage from BOTW2 would probably be central to the game/character added. BOTW Zelda was turned down at the beginning of development anyway, so I don’t really think they’d go back on that for a $5.99 character.
They could go with a Champion, but that assumes they’re looking at HW, and not BOTW. They may not even have a large role in BOTW2, which would make any of them a strange choice at that point.
It’s kinda one of those things where BOTW Link is still right there, and it seems like a character is being forced out of it for the sake of it. This isn’t to say a Champion wouldn’t be cool- I once stanned the option pre-“Everyone is here!”. That said, I think it’s a weird discussion to have.
Honestly I think the character would need to be added on their own merits, not to arbitrarily give Zelda a character, which is what it seems like folks are arguing. Zelda has plenty of excellent characters, so I can’t blame anybody for wanting them. I just think it’s far from a guarantee.