1. They kept supporting the 3DS because the Switch wasn't viewed as a direct successor to it. They'll drop support for the Switch like a sack of bricks when the successor comes out, just as they dropped the wii/ds when 3ds/wiiu came out, and basically every other console they've made. Nintendo only focus on the latest system.

2. The Switch wasn't backwards compatible, if you wanted to play 3ds games you need a 3ds, the switch successor should be backwards compatible so that will damage Switch sales once it's replacement comes out.

3. There was a big difference between 3ds and Switch. You could pick up a 3ds model for $100 while the Switch was $300, they catered to different markets with their different price points. The price difference between Switch and it's successor will probably be much smaller. I don't see the Switch getting price cuts to make it a valid purchase over Switch 2. Just like the PS4 hasn't been cut in price and isn't worth bothering with now.

Those are my reasons that I don't personally expect high Switch sales after it's replacement is released.  With a Switch 2 on the market there will be zero reason to buy a Switch unless they price the older console aggressively, which they won't.

Now for my expectations, 130m I guess.

Nintendo looks like it will bomb and everyone speaks of doom. Nintendo looks to do great and people have such absurd expectations that when they aren't met will look like a disappointment. The fact that they are guaranteed to do 110 million should have everyone marveling considering where we were last gen, anything beyond that is icing on the cake.

Basically yes, but with the current momentum, keeping up with last year for so long, anything below 130M would be disappointing because it would need a premature death for that.

lets say it's at 107 million this year(so 18 million for the second half of the year), next year it's unlikely to fall below 23 million with Splatoon 3, Breath of the Wild Sequel, Open World Pokemon - so we are looking at 130 million end of 2022. Even if a successor is launched at the end of 2023 I can see it surpassing 150 million, if a Successor launches after 2024 than its likely above 160 million. It all depends on what exactly are the plans for Nintendo - if it makes sense to prolong the life of the Switch until 2025 when they can offer something comparable to XSS performance on a handheld while still making a profit on hardware, I can see it trying to prolong the Switch until late 2024 early 2025.

So far they've launched a dock-less Switch - the Switch Lite, so the next possible iteration is a TV only Switch that acts as a supplementary computing & docking for Lites/OG/OLED Switches. Nintendo are already developing in a scalable way, that allows them to easily bump up resolution & fps on major titles, while it would be up to 3rd Parties to decide if it makes financial sense to update their existing games or leverage this option for future titles. This is how I think they can prolong the Switch's life and approach a crazy figure like 170 million. Basically the only chances of this happening is Switch 2 doesn't launch until 2025 and a Switch Pro is actually a complementary device that on it's own is just a TV only console with an empty Dock.

I am not too sure about the successor coming in 2023, let alone in spring. Breath 2 is almost guaranteed to come out in late 2022, but if it gets delayed I can see it releasing as a cross-gen game the next year, though I'm confident Nintendo is right on schedule now and we won't get the same sequence of events we had with the original game. That matters because, you know, Breath of the Wild was a huge factor in Switch's initial success. The regular models also haven't gotten a single price drop to this day, so there's room for the console to keep selling decently months after the successor was launched, even if it did in mid-2023 as you say. 

For whatever reason I also feel the Switch will also end up at 130M, but I still see it comfortably surpassing the 150M. 

I feel it will end at 130M, but nonetheless I don't discard that it has good possibilities for the 150M. 

145-155M

Incorrect.  The Switch is a successor to the 3DS and Wii U both.

They kept selling the 3DS, because they only had to support two systems during the transition, and that is easy for them to do.  Fun Fact: the NES got support even after the SNES released (and therefore kept selling), because Nintendo only had to support 3 systems at once, and so they still did it.  It's only when they are faced with supporting 4 systems at once do they pull the plug on the older systems immediately.  For example Gamecube, GBA, Wii and DS was too much for them to support all at once, so they Gamecube lost support immediately and the GBA got its life shortened as well.

When the Switch 2 comes, the original Switch will definitely get support, because Nintendo will only have 2 systems.  Also, the Switch is basically free money for them at this point, so it would be stupid to cancel support for it.  It will keep selling for years, even after the successor is released.  This is also ignoring the fact, that the 3DS actually had a system get down to $80 before they stopped making it.  Currently the cheapest Switch model is $200.  There is a whole lot of sales left to be had from bundles and price cuts.

Anyone predicting 130m at this point is on the extreme pessimistic side.  They see sales go down for a month or so without factoring in that people are waiting for the OLED model.  I am still expecting Switch sales to be up this year compared to 2020.  Switch sales during the holiday quarter of this year and going to blow away 2020 holiday sales.

I might add supporting both systems only works to keep sales steady  ​if the sequel system is seem as not worth it or if the sequel system has no BC

Sony keep supporting PS4 with software and third parties are all about cross gen games, but PS4 sales have plummeted. PS5 being full BC and smart delivery are making people go for it ASAP as there is no point buying a PS4 if all PS4 software can run on PS5

The question of whether Nintendo wants or not Switch to keep selling depends more on what they do for Switch 2 than what they do for current Switch

I think Nintendo wanting the same thing to happen (PS5 destroying PS4) is likely because again all big third parties will avoid commitment in Switch 2 until Switch 2 has a userbase big enough to justify their investment (I'm talking about AAA games here, like Monster Hunter Rise)

Nintendo strongly depends on their own games to cover their lack of third party blockbusters. Smaller third party titles and indies that can easily run on both Switch and Switch 2 won't make people buy Switch 2 to play games that don't need performance and graphics improvements in first place 

Hence Nintendo will need to artificially kill Switch support so Switch owners will feel the pressure to move on. 

Well, 150 million seems almost assured barring disaster. I voted 150-170 million.

It should be about 105 million end of this year. 2020 Calendar year it did about 27.37 million (28.83 was 2021 Fiscal Year). Half way through this calendar year it is about 220k units ahead of 2020, Q3 of this calendar year might put it tracking a bit behind last year, but the holiday season should be bigger with much bigger titles, new model, and not competing with the launch of two new systems, I could see it doing 27.5m to 28m this calendar year. What were the total numbers through last year, like 78 or 79 million? So Switch should end up this year at 105 or 106 million, let's say 105.

Next year will be a big year for major games. No doubt hardware sales will start to drop next year, let's say it still hits 22 million which shouldn't be too hard.

2023 we'll probably start to see price drops and the last round of major first party titles, let's say a drop to 18 million.

Say Switch gets a successor holiday 2024, which allows Switch to still sell like 12 million that year. That puts the Switch at 157 million (best selling system of all time) by end of 2024 just after its successor releases, and no doubt over the next few years in its retirement it'd easily pass 160 and probably get over 165 million. Even if successor comes out early like say Spring 2024 it'd still probably end up around 160 million. So I don't see any way it sells under 150 million. 170+ million could happen but only if Nintendo gets aggressive in its sales tactics (which they aren't known for doing), and like actually do lots of hardware and software price cuts and has a couple surprise big games planned late in Switch's life. So in the 160s seems very likely. And that's being slightly conservative, each year as outlined above could easily be a million or two higher than I'm estimating, so if successor launches holiday 2024 then finishing up a few years later at just over 170 is definitely possible.