Good call but by 2020 it was fairly obvious it was headed north of 30 mil. Now if the OP was made in 2017, that would be impressive.

More than 75% of voters said under 30m, so while it seems an easy bet to us now, that wasn't what people thought in 2020.

Looking at the game's Fiscal Year sales since release, (Special shoutout to @RolStoppable for providing the data , we see that Breath of the Wild has done this much thus far:

FY 03/2017 - 2.76 (2.76)
FY 03/2018 - 5.72 (8.48)
FY 03/2019 - 4.29 (12.77)
FY 03/2020 - 4.64 (17.41)

All signs point to Nintendo taking their time with releasing a successor, so the Switch still has plenty of life ahead of it. This is just a shot in the dark, but I could see future sales looking something like this:

FY 03/2021 - 3.70 (21.11)
FY 03/2022 - 4.00 (25.11) - I think Breath of the Wild 2 will release within this fiscal year, which will give a modest boost to the first game because you'll have people who want to play the first game before jumping into the 2nd one to understand the background behind it.

FY 03/2023 - 3.20 (28.31)
FY 03/2024 - 2.70 (31.01) - I think the Switch's successor will come out here. 7 years after the original released.

Keep in mind the Wii U version was at 1.67 million the last time Nintendo provided those figures. I'd imagine it would be around 2 million by the time Switch to comes out, (If it isn't already), bringing it to between 32.68 and 33.01 million

From there, it will only need an additional 1.99 to 2.32 million units to reach it. Which I think it would easily accomplish if that's the case.