I don't see much reason that BotW2 cannot release this year. This is a sequel, not a new game. The usual Zelda development span does not apply here.
No new game engine, no new combat engine, no new physics engine, no new A.I. engine. no new QA A.I. system, etc...
Very little new art assets, greatly enhanced code and system familiarity, QA A.I. script ready to go. And 3.5 years of dev time?
Seriously, what's a single, solid reason that prevents it from launching this Nov?
I'll give you the long explanation.