Dude it’s literally at 60 million 

I think a lot of people double dipped on the PS2 and DS when better versions hit the market. Nintendo is making it pretty hard to choose a Switch Lite over the standard Switch and even harder to own two systems based on crazy decisions like tying certain saves to a single system.

A sleeker model would boost sales into that territory but I don't see one on the horizon based on the news I've seen so far.

Best selling Nintendo console? Yes. Best selling console? Impossible.

It doesn't need to sell 20 million for the next 5 years. This fiscal year it will probably hit 25 million, next year will be another 22 or so million (I think the next generation systems are not going to "fly off of shelves") so that would put it at 100 million units in 5 years. Figure another 35 million in years 6 and 7 and then it tappers off with roughly 20 million at the end of it's life. Even when they come out with a next gen Switch the original Switch will still be in demand because of it's library.

This isn't a normal console and Nintendo will be in no hurry to replace it, just a couple more refreshes and price cuts.

Quoted twice, 🤔

In any case, I think you're right about the PS5 and XSX. I think we're gonna be faced with a 3DS/Vita situation. Scalpers are gonna buy a ton of them and they're gonna initially sell well but things are gonna die down quickly in 2021. Just not feeling the hype, yet.

My guess is 90 to 180 millions.
What do we have for next Christmas already ?...

The most likely scenario is that Switch will become the best selling console of all time.  This year is going to be it's peak year, and it's going to peak higher than any home system ever has.  The only system with a higher peak would be the DS, and it's sales fell extremely quickly after it's peak (basically it fell harder than any successful system ever has).  All Switch needs is a somewhat gradual descent in sales after it's peak and it will coast right into the #1 position.  Mathematically it's very feasible.  It's peaking later and higher than the PS2, so it is set up very well to outsell the PS2.  Or if you want to compare it to the DS, then it just needs a gradual descent, and it will ousell the DS.  

People say "the stars need to align" in order for this to happen.  Well, let's actually look at what would needs to happen for the "stars to align" on the most successful system ever and see if that is happening for the Switch.  Since DS is the big selling Nintendo system, let's compare Switch and DS.  Here is what would need to happen for a Nintendo system to surpass the DS.

1. Incredible First Party Software. Check.  Switch easily has this category down.  Compare the first party line-up of the Switch and DS.  Both had evergreens, but Switch evergreens are actually core Nintendo titles.  Zelda and Smash were never considered evergreens before.  Now they are.  Mario Kart 8 has already outsold Mario Kart DS and it's still going strong.  Animal Crossing is heading like it's going to sell 3-4 times what the DS version sold, which is crazy.  We can safely add in 2 more Pokemon games and another mainline Zelda before the Switch is done and several more years of other first party titles.  DS had amazing first party sales, but Switch is totally blowing it away.
2. Lots of 3rd Party Support.  Check.  DS had 1985 games.  Switch already has 2665 games.  Conservatively speaking, we can double that and Switch is going to have at least 5000 games by the time it is done selling.  However, so far each year Switch gets more third party releases than the last.  Most likely Switch will have 7000 games (or more) by the time it's all said and done.  It totally blows the DS away here too.
3. Cheapest System During a Recession.  Check.  DS sales peaked during the 2008 calendar year which is when a major global recession hit.  It was also the cheapest current system on the market.  Switch will be the cheapest current system on the market when the PS5 and Series X launch, and there is a major recession looming.  Since I live in the US, I've only been looking at US financial metrics, but here it appears this recession is going to make 2008 look like a cakewalk.
4. Room for Revisions and Price Cuts.  Check.  Switch has only had one major revision, the Switch Lite, and ironically the base model is the more popular system.  Switch has also had no price cuts.  We are almost 3.5 years after the launch of the Switch, and it's in short supply in many places and it still hasn't had a price cut yet.  It isn't even holiday season either.  That is unprecendented.  People are waiting for Switch to do something unprecedented.  It's doing it right now.  No system has ever gone this long without a pricecut, and it isn't going to get one soon, because it's sold out in so many places.  Switch has so much room to introduce revisions and price cuts and it doesn't have to do this anytime soon.  Meanwhile, the DS actually was being outsold by the PSP when it first launched.  It didn't start selling like crazy until after it's first revision.  Since the base Switch model is in short supply 3.5 years after launch, it is blowing away the DS here too.

In short, the stars are aligning for the Switch.  It needs the stars to align and they most definitely are.  When you compare the Switch to other successful systems it's peaking later and higher than everything but the DS, which peaked around the same time but higher.  The DS also crashed hard after it's peak and still became the 2nd best selling system of all time (not far behind the PS2).  All Switch needs to do is to not crash hard.  It just needs a gradual decline in sales each year after this one.  How can it do that?  Solid first party evergreens, lots of third party games, be the cheapest option during a recession, and have lots of room for revisions and price cuts.  It has all of that.  It's set up to sell better than the DS by a fair margin.

The Switch is set up to be the best selling system of all time.  This is actually the likely scenario.

Also PS2 (along with PS1) had lots of hardware issues, there were plenty of people who had to buy second or even third PS2's because they broke easily. Not to mention the fact that lots of people bought PS2 simply to use as a dvd player because it was actually a cheap dvd player back then. Switch has neither of those things to help drive extra sales.

Switch will get some of the buying new versions or buying multiple versions (like a family that has OG and then a Lite for kids), but it will definitely be less pronounced since Switch is more expensive than previous handhelds so people aren't just gonna be buying multiple Switches just cuz. When a premium Switch comes out I could see a lot of Switch owners from like 2017/2018 upgrading (I might) but yeah in general Switch doesn't have the buy multiple versions thing going for it as well as DS because it is more expensive and doesn't have the system breaking hardware issues or the DVD reason that PS2 had to expand sales. That makes it very hard for any system to reach those 150-something numbers those two systems hit.

Yep!  I guarantee Microsoft and Sony are sweating bullets right now between the smash success that the Switch is and the looming recession/global lockdowns.  With the amazing lineup of games that the Switch has it is just a much more appealing option for the next couple years on that alone.  I bet many households will be looking at this scenario come the holidays as well:

Scenario 1: Buy a Switch/Lite, maybe a Pro Controller, and MK8/Pokemon/Animal Crossing/etc for $300 to $400...

Scenario 2: Buy this $500 system and another $50+ for a single game... that's pushing $600...

I just foresee scenario 1 being much more appealing to many in the coming months/years.

Nope, sales curve is pretty consistent, you can see it increase, plateau, descrease and dwindle. If platform holders really could keep the same system selling they wouldn't take the risk to put a new system on the market with 0 install base and games. They usually launch the new system when the current gen console SW sales start to decrease. You can look at PS4, HW sales have started dropping for about 2 years, but SW was still good, but you can see it is nearing the drop as well. Why do you think if Sony kept it around for let's say another 10 years it would sell another 100M?