I voted 27-30mil. With Switch's life ending in the next 12-18 months people will be focusing their attention on the next system so that'll hurt TotK's legs a bit.
It should hit 20m this year, maybe be there before the holiday quarter even starts. Wouldn't be surprised if it passes 20m during the summer quarter. And it should do well over the holidays, but I think by next year it'll be selling 1mil per quarter tops. Maybe it's at 27-28m by end of 2024 with the next gen system out. And it'll continue to get a trickle of sales, especially assuming next gen is backwards compatible. But I don't see that being enough to pass 30m. I expect it'll finish some 5 million behind BotW.