Saturation effects start to kick in when a system has approximately half of its lifetime sales.  This is also when the system peaks.  It still remains to be seen if Switch will peak in Japan in 2020 or 2021.  However, given how close the two year end totals will be, I'd say the theoretical peak was sometime earlier this year.  If Switch's peak was in 2020, then double it's LTD for end of 2020 and add a few million.  If Switch's peak was in 2021, then double the 2021 LTD and subtract a few million.  That gives a pretty good ballpark of what Switch's lifetime sales will be.

50% drops every year (assuming 6mil this year)

2022: 3mil

2023: 1.5mil

2024+: 750k

lifetime 30mil lifetime

And why would Microsoft keep sending those units to a country where people are supposedly not buying them instead of sending them directly to those countries where people are willing to pay "1.5-2x the MSRP price"?

If sales start to dip (33%) to 4 million in 2022 in Japan then 2021 is the second and last time the switch will sell 25m in a calendar year. 2022 will be close to 2019 numbers.

Hardware and Software are linked, saturation argument doesn't take into account the absence of competition in terms of where hit software is hitting. Right now 2022 is looking like the Software peak for the Switch. 

Splatoon 3 I'm betting will surpass 4 million physical sales in just 2022, I think it's one of the biggest guns the Switch has up its sleave

YEAR ONE PHYSICAL SALES

TOTAL SALES / LTD TOTAL HARDWARE / ATTACH RATE

Splatoon - 1.064.897 / 2.999.282 / 35.5%

Splatoon 2 - 1.752.096 / 3.407.158 / 51.4%

As we see the launch years of Splatoon on the Wii U and Switch weren't special in terms of software numbers but the attach rate is insane. Especially as we consider that at least 15% of those sales on Wii U were actually digital and over 20% of Splatoon 2. Now with a 23 million user-base Splatoon 3 is the first time the launch sales would be in the region of 5 million with digital due to vouchers. It's potentially the only title to be able to compete with New Horizon in Japan and we know what type of impact that had on last year's demand for the Switch. Like New Horizon it will also benefit by future updates that should continue for at least two years, so become a 10 million title is certainly possible based on reception in Japan. 

I honestly believe that the franchise continues to be underestimated as a hardware mover. It helped the Wii U of all things see growth in 2015, while it was a key game for the run away success of the Switch in Japan with over 50% of year-one buyers also purchasing Splatoon 2. The launch I think will be over 2 million physical and the biggest hardware week since the launch of New Horizon when Switch managed 392K

The marketing hasn't even kicked in, but when it does it will be everywhere in Japan. Global Testfires will be key and this will be the real challenge for Nintendo, they have never had to deal with a launch of some many concurrent users World Wide. Otherwise in terms of gameplay I'm pretty confident with the quality, so far for Splatoon & Splatoon 2 are by far the most innovative things that have happened to the genre in over 20-30 years. The team behind it has had five years to bring new ideas to the fold both in terms of PvP, PvE and Single Player. 

The stars are aligning for Splatoon 3 launch to be a major milestone for the Nintendo. Right now the reveal is the most viewed direct/e3 trailer on NintendoJp's channel this year and the #5 most viewed direct/e3 trailer of all time with over 5.6 million views in less than an year. The SplatoonJP twitter account is the #3rd most followed Nintendo account in Japan. The game is going to be huge hit 

I don't see the Switch having a chance of reaching the high 30's but if it does over 5 million next year it'll start to seem possible. I look at the DS and see that once it got past 20 million sales slowed down a lot with a large drop in 2008 so the Switch doing around 4 million next year seems likely to me.

I compare to the DS, since people expect DS numbers, 33m.

The 3DS had an artificial sales curve due to the first year price cut. But it still represents just how hard consoles may drop in Japan.

NSW year 7 and 8 probably won't be that good either as the next successor should be announced by then.

You also need to take a look at the lineup for the system. 

2022 Switch

Splatoon = 4-5M seller

Pokemon Legends = 3-4M seller

Botw 2 - 2.5M seller

3D Kirby game - 1.5M seller

MHR SunBreak - 1M seller

And many more

Man, you’re expecting an awful lot out of Kirby.

Kirby is quite popular in Japan with digital the prior game in Kirby AS on Switched crossed 1m in Japan which is a series average in the region so 1.5m for the first full 3D entry is very possible.