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.

You've gone too far this time you madman.

I can see 30 million happening but not sure about 35 million.

I’m still confused to why people think Breath Of The Wild 2 will take away the sales of the original?

Why and for what reason? If anything one will continue to sell more than 2 lol because the fact of the earlier release plus added hype of the sequel release.

Can somebody explain the logic? I would understand if the sequel would be like the sims 1 > 2 > 3 > 4 or fifa or madden or Pokémon. Which are mostly the same game with the same gameplay loop with added content or changed aesthetic.

People don’t have to buy earlier versions because the new game improved on everything. But Zeldas have never been like that. Each games has been different games with different stories and gameplay?

That’s like saying Final Fantasy 16 release will take away sales from Final Fantasy 14. Does that make sense to y’all? Or Resident Evil 2 remake took away sales from 7 lol

the WiiU version has done its duty at 2mil.

the Switch version will definitely pass the 20million mark by the end of the year. over 25 is a given at this point but passing 30mil is all up to when BOTW2 is going to be released.

 BotW2 will push sales not make them stop. Also like SMG to SMg2 I’m betting on BotW budget release

Now I'm going bold to predict 25m LTD and defy Tbone.