I'll go safe and say early 2021

Mid to late 2021 seems to be the most logical timeframe.
If it was 2020 they would have announced that information and 2022 might be unrealistic because they utilize the same engine used in botw and can reuse a lot of assets.

Late 2020. BotW would have released in late 2015 (three years of full development) if it wasn't for Nintendo having problems with the game's physics engine and later deciding to port it over to the Switch. If they're reusing the engine and a lot of the assets from the original then it's not unreasonable to assume a 2020 holiday release.

Early 2021, March or April most likely.

I think something different will be the big Holiday 2020 title. The fact that we have no title or release year yet, a 2020 release doesn't seem likely.

I'm not going to predict, but I will say that the latest it could release with me still being ok with such an early announcement is Early 2021 (Jan-April), maybe pushing that into the later part of the first half of the year (May-June), but that's still pushing it. I'm pretty sure Breath of the Wild, Skyward Sword, and Twilight Princess were all about 2.5 years away from release when they got their first trailers. But given that Breath of the Wild's map is already done, the engine is done, most of the models and animations are done ... that seems like too long of a wait.

Also, I could have sworn that there was some pretty obvious evidence that they were making a new Zelda back in 2018, so damning that even it being a unconfirmed didn't really matter, but it seems like I can't find it, and most of the info around is from early 2019 (when Monolith Soft had their hiring spree). 

Late 2020.

They're re-using the engine and assets from BotW. And they've probably been working on it for more than a year. There's no reason for it to come later than next year.

So that's my bet.

hopefully asap

i'm going to be super optimistic and say late 2020. early 2020 would be awesome if it were the anniversary of botw. My intuition tells me that cutscenes would be one of the last elements they'd be working on and that trailer seemed to be a compilation of multiple cutscenes. Here's hopin.

i dunno holiday 2020 sounds more like nintendo lol

Late 2022. I'm not taking any risks getting my hopes up for a release any sooner than that.

I bought a WiiU for BOTW when they first showed the trailer for that in 2014. It didn't show up for 3 more years.

https://www.youtube.com/watch?v=XZmxvig1dXE