If we are talking fiscal years, then I'd say 4 at 20m+ is almost guaranteed. Demand for OLED is going to be high for several months (at least) next year, and the software lineup looks to make 2022 one of Switch's best years.
That fifth year though...I think it will really depend on if/when Nintendo makes a price cut. The reality is that they would look great to their investors if they could pull off a fifth year at 20m+. However, they might wait for sales to drop more than that before they actually issue a price cut. Basically, I think that fifth year at 20m+ is possible, but it depends a lot on Nintendo's behavior.
curl-6 bet me that PS5 + X|S sales would reach 56m before year end 2023 and he was right.
My Bet With curl-6
My Threads:
Master Thread, Game of the Year/Decade
Switch Will Be #1 All Time
Zelda Will Outsell Mario (Achieved)
How Much Will MH Rise sell?
My Bet With Metallox
