True. Am I the only one that expects a sequel to take under 4 years? BotW2 could have been out in 2019, similar to how Majora's Mask quickly followed up Ocarina of Time. BotW2 is taking so long to make that I won't be satisfied unless it massively builds on the first game. A simple paint by numbers sequel isn't going to cut it anymore.
I'm sure internally it was probably at some point planned for 2021 release. Considering most assets are already created I would not expect for it to take too long. But, I guess if it all depends on what the earthquake in the trailer meant. Whether Hyrule castle is being transported to another land or if the earthquake is just an excuse to change the layout of the existing map. Designing a new map layout will take time.