I'd say holiday season 2021.
While they can reuse many assets, the scope of the game is just much greater than Majoras Mask was, They also have not even a name for it yet, so I doubt they could bring it out for 2020, there's just too much to do until then.
It could also release for Goldenweek/Obon Week, but I expect it to be more of the game Nintendo wants to push holiday sales with.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454 List as Google Doc: https://docs.google.com/spreadsheets/d/1aW2hXQT1TheElVS7z-F3pP-7nbqdrDqWNTxl6JoJWBY/edit?usp=sharing
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/
Free Pc Games thread: https://gamrconnect.vgchartz.com/thread/248138/free-pc-games/1/
