This FY and next FY are going to be the most important for determining how well this prediction is doing.  Switch total shipments for the FY ending March 2020 were 55.78m.  This FY is going to be the peak and the year after will show us how much of a hold (or drop) Switch is getting after its peak.  Once we see the next two years then it will be a lot more clear how the Switch is going to do.

Optimistic case: High peak and strong hold.  Maybe something like 30m this FY and 25m next FY.  That would put Switch at essentially 111m at March 2022.  Now assume around 30% drops after that and get approx. 17.5m, 12m, 8.5m and another 20-30m in the following years and you get 169m-179m.  Basically in this scenario with a high peak and a strong hold it's pretty easy for Switch to take the top spot.

Pessimistic case: Lower peak and a big drop.  Let's say Switch ships 24m this FY and 15m next FY.  This puts Switch at about 95m at March 2022.  Assume 40% drops and get approx.  9m, 5m, and another 15-25m in the following years.  That puts the total at 124m-134m.  With a low peak this FY and a big drop next FY, then there is no way the Switch can take the top spot.

If we get one of the two other cases, then it's going to be a close battle to the end.
Low peak, strong hold:  This is probably what will happen if Nintendo doesn't manufacture enough and a lot of shipments spill over to the following FY.  Imagine something like 24m this year and 22m next year.  That's a pretty low YoY drop, and then we'll just have to keep collecting data and it will be close until the end.

High peak, big drop:  This is a very likely scenario.  Something like 30m this FY and 20m next FY.  This means COVID gave Switch a huge boost, but 20m at the end of March 2022 is still a solid number, since this is close to shipments from the March 2020 FY.  Total would be 106m at that point, and then we'd have to carefully watch the legs, because it's going to be close.  25% drops would be close to 15m, 11m, 8m with another 20-30m after that.  Total 160m-170m.  On the other hand 40% drops would be more like 12m, 7m and then 15-25m after that which totals.  140m-150m.

In this last case you can see that 25% drops put it just above the record while 40% drops put it just below the record.  So in this situation it very much comes down to how well Switch can leg it out.  Low peak, strong hold is not much diffferent.  But if we get one of the first two scenarios, then the data will be pretty conclusive about whether or not Switch will break the record.

Umm why are your post-Switch2 launch totals so crazy high for Switch? Your pessimistic number for Switch sales after the successor launches is 15-25 million??? Pessimistic should be like 5-7 million, not up to 25 million, and optimistic should be like 15 million tops, not up to 30 million.

I think your low peak, strong hold scenario is probably most correct, just because I don't think Nintendo is gonna make enough Switch's to get anywhere near 30 million, more like 25 million. Or maybe a better way to put it is low peak (ha I like how ~25 million is "low" in this context) and gradual drop. Unless they have vastly increased production and we just aren't aware of it, I mean they should be doing that but until I see some statement by them or until we see that they don't have massive holiday shortages I'm gonna assume they aren't producing 30 million systems this fiscal year. But if they've massively upped their manufacturing so that they are still healthily building up for a huge holiday quarter despite shipping tons of systems during the year then obviously they will go higher than 25 million.

Anyway, I think fiscal years of ~25, ~20, ~16, ~10 (leading up to Switch2 launch), and then 10 million post-Switch2 launch are reasonable. Let's see that puts it at 136+ million lifetime, which is very realistic. If they can actually put 30 million systems into stores this fiscal year then maybe they break 140 million.

3DS has shipped 9.65m total for the past 3 fiscal years.  After this FY that will probably go up to around 10m total which will be 13.1% of its lifetime sales.  On my optimistic range I'm saying the post "Switch 2" launch as 11.8% to 16.8% which would be in line with 3DS tail end sales.  On the pessimistic estimate I have the tail end as 12.1% to 18.7%.  The 3DS fits in their too, but maybe 15m-20m would be even more precise than 15m-25m.  Either way it doesn't change my analysis.  If Switch sells low this year and has a big drop next year, then it's definitely not going to be the best selling system of all time.  And if the next two years are remarkably high, then my analysis doesn't change and Switch is extremely likely to break the record.

Your last paragraph is actually on the pessimistic side.  If Nintendo doesn't produce enough this FY, then it's going to ship almost as much the next FY (or maybe more).  It's going to have to ship a lot just to get retail inventories back up to where they normally are, not to mention satisfying backed up demand.  Also your tail end is on the small side.  At any rate, this is all kind of paper napkin analysis, and this sort of scenario very much comes down to what kind of legs Switch has.  The average for "low peak, strong hold" being around 150m or so, but it can easily swing up or down +/-20m depending on a variety of factors.

I'm posting this here, because the poll at 13:45 shows most people think Switch will outsell the DS.  About a year ago, the talk I saw on Youtube videos was more like, "Hey, I think this thing can outsell the Wii".  Now the talk is more like "it can outsell the DS" or "it will be the best selling system of all time".

https://youtu.be/5aJXSieH2aQ?t=825

I'm sticking by my expressed opinion I've had for a long time on this: It all depends on when Switch 2 launches. If Switch 2 launches March 2023 (6 years after Switch 1), it won't happen. If they push it back to 7 years after Switch 1 (March 2024) and if, by doing so, they release huge games in great abundance through winter 2023, then I do think it's likely it could beat the DS.

Wii tanked towards the end because software dried up due to them working on Wii U/3DS games. Based on this, if Switch 1 lasts 6 years before Switch 2, I expect only 5 of those years to have the quantity of quality games we expect, whereas the last year will be somewhat dry. But if they push it back to 7 years, that extra year (6 now) of large amounts of quality games will push them over the DS edge I think.

And all this depends on if the rumors of Switch Pro are true and, if so, when it launches. Historically, Nintendo has released a successor device 1.5-2 years after the release of an upgraded current generation device. So, if they were to release the Switch Pro today, that means Switch 2 won't come out until somewhere between 6/16/22 - 12/16/22. Obviously they would have to build hype for the Pro with marketing so they wouldn't shadow release it. If they don't announce the Pro soon and release it within a few months after announcing it, I am convinced that is a sign Nintendo plans on extending Switch 1 life to 7 full years of no competition from Switch 2 and they have huge plans for the second half of Switch 1's life.

It's happening

Lol, not sure if this is what you were referencing, but it reminds me of this scene from poltergeist.

Haha, not really, I meant exactly what I said: It's happening, Switch is becoming the best selling console ever released 

Well its under 80mill, it needs 70+ mill to sell better then the ps2 and nds, its 5 years old.

Also, why is the switch lite being considert a console? Its a deticated handheld.

Enters now in the 5th year.

Console launch  is march 3 2017. Do the math

Console in a broad way, it's not only stationary and not only handheld, its a hybrid.