This will a interesting thread.

When you look at the numbers broken down by region you can clearly see that the Switch is within striking distance. Very doable my friends!!

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.

It won't.

See ya in two years.

I doubt they will keep the Switch on the market as long as the 3DS when the successor comes out. Wii U was a massive failure and 3DS was the system keeping them afloat. Switch wasn't necessarily going to pick up immediately, so the 3DS was kept around to assure some kind of cushion in case they need it. 

Successor will probably be a Switch 2.0, so why would they keep the cheap regular model on the market as long. That's why i don't see the successor for a while unless they count it as a successor and a part of the Switch family, which is something they have been hinting at.

One Year would be enough to see Nintendo 2023 Games Line Up and tell if they really want to keep the Switch alive or they are getting ready for Switch 2.0.

This year Switch is going to finish close to 130m, so another 30m+ even 40m+ would start making more sence.

3DS Sold another 20m after Switch Trailer was revealed in October 2016 and it didn't even reach 7m sold that year.

This is my type of topic.

Should I take the OP as an official prediction then?

Japan: ~10m more, so ~35m LTD
Americas: ~20m more, so ~60m LTD
Europe: ~20m more, so ~47m LTD
Other: ~10m more, so ~22m LTD

I would have been skeptical this would be possible until Nintendo’s quarterly earnings call this week. Nintendo said that the switch was “midway” through its life. Midway, as in not nearing the end. They clearly plan to support the console for several more years.

A scenario where it turns out they were joking and a switch successor is launching in 2023 would be the only way a “cliff” could materialize, I think

I'm hopeful that it could happen. Really depends on when a successor launches. The earliest I could see a successor launch in which Switch reaches lifetime sales of 160 million would be Holiday 2024 (which is when I'm personally hoping Switch 2 launches). Anything earlier than that and I can't see Switch reach 160m. Anything later and it just becomes easier.

It's also still possible for the successor to launch in Holiday 2024 and for the Switch to fall short of 160m and even fall short of passing DS & PS2.

Possible but I don't think Nintendo will keep Switch going for long enough.

That said, there is a clear path to make this happen. Don't launch successor until holiday 2025.
And in the meantime actually do hardware price cuts in the final years, do one more new model revision, and load up on the games including MK9 on Switch instead of as a launch title for the successor. There's a ton of games people are still waiting for and wanting that could easily fill up a few more years with big releases. Combine that with the aforementioned price cuts and new model, and do the Nintendo Select's game discounts dropping a ton of older Switch 1st party games to $30. I bet plenty of '17/'18 Switch owners would pick up a newer model Switch either OLED or the hypothetical next model if Nintendo makes it clear (by doing another model and releasing MK9 on Switch) that the Switch is staying passed 2024.

In a word, all they'd have to do is get aggressive. They haven't actually tried to be aggressive in several generations, and with the Switch they haven't needed to because it still crushes the competition after 5 years, but they could totally get to 160m by being aggressive from 2023 to 2025 with their Switch business strategy.

More likely though they'll end the Switch a bit early in 2024 and let it die off in the 140 millions. But who knows maybe they are actually serious about a really long life for Switch like they keep telling us every year.