It's tough. It's making me think back to some of the Wii U days. The difference though is that the Switch has had far more third-party titles (even if there is a lot of shovelware), has some Wii U ports, and has had very acclaimed new first-party games.
I really don't know what Nintendo software to expect this year. The next Zelda could come out in November, but it's very likely to not release until 2021. We get Mario games every year, so we might get Mario Golf or perhaps even Super Mario Odyssey 2. Maybe even a new Paper Mario in the style of the first two.
Lifetime Sales Predictions
Switch: 144 million (was 73, then 96, then 113 million, then 125 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima