Last edited by PAOerfulone - on 18 June 2019
Because the game is reusing Breath of the Wild's engine and assets, that cuts out a good chunk of the development time. Because of that, I think they're already much farther along with this game than compared to how far they were with Breath of the Wild when it was first revealed at E3 2014.
Even though they didn't announce a date, I think that the development team is internally targeting a Holiday 2020 release. But, I expect it to be delayed, because it's 3D Zelda. It always gets delayed. That, and I believe the next 3D Mario game will be the big holiday title for 2020.