Switch will reach 80 million sales.

How many years do you think Nintendo will be supporting the Switch until a Switch 2 (?)

6 or 7 years imo. 

This is really the root of why we disagree.  I think that killer apps are a lot more important than you do.  A vast and diverse library is certainly important, but how does one get that?  A killer app released during the console's first year or so leads 3rd parties to want to make games for the console.  The killer app builds sales momentum, and then the other games keep the sales momentum going.

Reasonable assumptions for this question for any console are 5-7 years. Nintendo targets currently 14M console for the first full financial year. As practically never the first year is the peak year (usually year 2-4) and not the worst either, it is not the worst assumption to put that as the average until the successor is released.

14M*5=70M

14M*6=84M

14M*7=98M

So 80M isn't at all unreasonable. In the contrary, a number much lower would have to be explained at this point, as this obviously assumes an unusual lifecycle. So, how many years do you think until Switch 2 and which year will be peak in your assumption?

The distinction is important too, because you want a killer app early on to make money on the vast and diverse library later in the lifecycle.

I think thats possible. Maybe 5-6 years though for me.

2017: Switch releases

2018: Status quo

2019: Switch-Mini releases (removes less important features, the included dock, possibly smaller device, etc. ways to lessen the price by $100-150 compared to regular Switch)

2020: Switch price drop by $50-100

2021: Status quo. With maybe a Switch 2 announcement.

2022: Switch 2 releases with a Tegra X(number) from Nvidia that is fully backwards compatible with OG Switch games.

The disagreement comes from you using personal bias over sales to determine if a game is a killer app or not. However if you truely believe the bolded now (which is what I've been trying to get through to you...), a complete 180 from your previous stance where BotW is solely responsible for Switch's success, then surely you can no longer agree with your Switch selling less in 2018 claim. Even if you don't believe Splatoon/3D Mario/Mario Kart are killer apps despite sales clearly saying otherwise, they along with the many other games are going to maintain momentum. Also another tidbit I shoulda brought up earlier is that pretty much no console has ever slowed down in the second year, yep even the Wii U's year 2 was better than it's 1st. Switch has arguably the best library ever for a system going into year 2, no way will it be an exception to this.

Ugh I said I was gonna drop this but with the bolded you showed signs of getting what I'm saying so I felt compelled enough to give a lengthly reply. Don't let me down now with your next response if you make one!

Not a 180 at all.  Let me be clear what my stance is, then you can go back to my original post and see if I am contradicting myself.

1) This year, 2017, the Switch is selling well because of two factors: A) People who want a powerful handheld and B) Zelda.

2) In 2018, sales will decline compared to 2017, because the momentum from Zelda will have worn off.

3) In 2019+, sales will dramatically rise because new groups of people will hop on board the Switch.  This will be because of things like a larger library (i.e. many 3rd parties) and cheaper/simpler hardware.

Also, here is a bonus for you. :)  Switch's year 2 will be different from every other console, because Switch's year 1 was different from every other console.  Name another console that both launched early in the year and sold far beyond nearly everyone's expectations.

Yep you said Zelda momentum (which implys Zelda is the sole cause of momentum, a conclusion only possible using personal bias) is gonna suddenly wear off for reasons you've yet to explain, despite the many other games that you just said will keep the momentum up.

Why should I name one? You're the one implying launching early and exceeding expectations somehow means a worse 2nd year, so you need to provide proof of that. There is none of course, as that logic just doesn't make any sense. Every majorly successful console exceeds expectations so I can't even begin to see how that would mean suddenly selling worse. Infact when expectations are exceeded to the point of supply constraints as is the case with Switch, that only means seling more next year is practically guaranteed.