PS4 looked unstoppable, but look now, it's stopping!
Anyway thinking NS wouldn't reach 120M was ridiculous, last January NS was regularly outselling PS4 since the end of August 2019 and it was already clear that PS4 sales were past its peak and slowing down, and if it won lifetime it would have been by a few millions. The biggest chance for PS4 already was the possibility of Ninty conceding NS a shorter life.

What the heck, I'll go for a 3 year sweep:

End of 2020 - Switch passes 3DS (achieved)
End of 2021 - Switch passes Wii (likely)
End of 2022 - Switch passes PS4 (my prediction)

Well, if the Switch does have it's peak year as year 4/5, that actually is similar to how past patterns have gone to be fair. Just, more similar to Gameboy and DS  

(Think 3DS peaked year 3?) 

In before haters claim that if the Switch only breaks 20 mil in 2021, it already peaked and the sales clearly fell off a cliff ensuring that it will fall short of PS4.

Does it make a difference if it does? PS4 also has PS5 sales but then you have to factor that XBOX sales. Nintendo systems have shown time and time again that only first-party sells. Sure the occasional third-party title becomes God's gift to humanity when it comes to Nintendo, but on the whole Nintendo fans are all about Nintendo.

It is another Wii situation, just wait till it outsells the 360 and all the third-party will flock to it! Except they didn't, and then the sales fell of a cliff once the novelty wore off.

Considering the PS4 struggles to reach 120M, I would say that if the Switch passes the Wii this year, then it's practically guaranteed to pass the PS4 next year. After all, but consoles are only separated by 13M so far, and I doubt there will be many more to come.

GB, NES, Super NEs, DS, 3DS, Wii and Switch disagree 

The top selling Street Fighter is on Super Nes.

best selling Tetris games is on Nintendo console

best selling Ubisoft single SKU is on Nintendo console. 

Level 5 make big buck of money on DS and 3DS ( Professor Layton, Inazuma, Yokai Watch) 3M+ sellers.

Dragon Quest best single SKU also on Nintendo Console.

A great percentage of indies sells better on Nintendo Switch.

Momotaro sell 2M+ on Switch. 

This is just such a weird argument right now. Like yeah, the first party games are the main attraction of Nintendo consoles, but the Switch is having the best third party support from a Nintendo console since the Snes,and far better than the Wii had. And we already got so many articles and news about third parties and indies selling well on the console...

We have another cliff theorist! :O

Also, you're wrong and the good thing is, we don't have to wait long until you're proven so.

Also think about last year. It only took one game to carry the Switch the entire year. That along with people are probably now seeing to big appeal of the Switch, and also it's the cheapest system on the market. There is a good chance 2021 will be peak year, which would make sales go above Wii and PS1. So if that happens I think it will outsell PS4 in late 2022. Of course PS4 is still selling, but it's sales are dropping harder than what anyone predicted (is this another Wii situation?).