Seeing so many say delay or late 2021 and so on, makes me think of when Super Mario Odyssey and Xenoblade 2 were both announced with their dates and the 90% of people who all said "No way they will keep those date, delay imminent."
Or those that said Animal Crossing would be delayed and it was.
Both Mario and XC2 were shown with early gameplay when they got their release date at first, Animal Crossing didn't. It was just a logo.
Here we already got what I'd call the intro portion of the game in this teaser for BOTW 2, so I'm guessing they're actually further in developpement than most people think so that's why I'll state that they need a big holiday launcher next year.
Honestly though, I'd prefer them to launch it on March 2021 to coincide with the release of BOTW too.
I mean, if BOTW 2 is announced as their next focused title for E3 2020, easy to predict where it'll land itself ;)