It's doable. 1.5 to 2 years ago I would've said it's too high of a prediction. And 4 years or more ago I would've called it hysterical and pretty much pie in the sky.
Nintendo is a very tough to corporation to predict regarding their software, hardware, services, etc. They could already release Switch 2 in mid to late 2023 for all we know and give Switch the 3DS treatment you mentioned at best. And if Switch is already replaced in the second half of 2023, it will probably finish around 130-140 million. But if it's replaced in March 2024 like I think it will be, it will probably finish with 140-150 million or so units sold.
My point is that Switch will probably sell around 10 million units once its successor launches because Nintendo will likely want to focus as much manufacturing on Switch 2 and Switch 2 will probably be popular right out of the gate.
Lifetime Sales Predictions
Switch: 151 million (was 73, then 96, then 113 million, then 125 million, then 144 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 67 million (was 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