I agree with this, which is obviously a very good result.

The thing is DS had such extraordinary high yearly sales and PS2 had such an extraordinary long life that I doubt anything can ever match that. PS4 had such a flawless generation yet still doesn’t come near the two at the top.

Not impossible but quite unlikely.

No. 3rd best

There could be a chance, if the current system will be supported by Nintendo a long time after its successor will be released. The current model could then be sold at $ 149 - 199, the Switch Lite at $ 99 and the successor in a similar range like the current model now (between $ 300 - 400. This should mean that a few games will be released cross-gen. Nintendo usually don't do this a long time, if at all.

So its depending on Nintendo's strategy. I see a small chance.

No chance IMO but what do i know

My guess is that Nintendo will come up with a line of compatible Switch consoles (like the Gameboy/Color/DS/3DS), so no one of them will be the best seller... but the sum of all combined will be huge.

As a console, NO.
Consoles are dedicated gaming machines. The Switch is neither a console nor a handheld, but a hybrid of the two.
As a hybrid, in theory can capitalize into the handheld segment for sales, specially with the lite version, but even then when combined as a whole I don't see it selling more than 120-130 Millions, due to the fact that by the time it does (2023-2024) a Switch successor should start to opaque Switch1 sales.

Surpassing the Wii seems plausible, and surpassing the GB seems difficult but posible. No way it's surpassing the DS, that level of sales is difficult without the stars aligning.

To think when I said Switch would sell Wii-like numbers, I was laughed at. My, how the tides have turned.

It certainly isn't impossible, but everything would need to line up just right.
I've considered before what kind of sales trajectory it would need to reach that and unless 2020-2022 become three miracle years like the DS did in 2007-2009, I think it can only happen if the next Ninty console doesn't come out til 2025, and even then it would require some damn good years until then.

My current prediction is the slightly-less-but-still-quite ambitious 140-150 mil.