It will most likely live on for longer than 5 years guys. Even the 3DS which was limited af since launch is turning 7 in 2 months.
60 million would be pretty bad imo after being the best selling console of all time on its first year, that we can 80% say its happening, it would need to drop like a rock in year 3-4 or not be able to pick up yoy after its first one while having Smash, Pokemon, Labo, Mario 2D, Animal crossing, price cut, better deals and bundles and probably a revision. That's insane to me. If it is (most likely) selling around 15 millions in a launch year, without most of the big system sellers and marketing boost, there is no way it won't make it to alteast 80 millions imo.
To me, 80 millions is literally the worst case scenario of it's lifetime sales. But seeing how its outselling Wii, it will have both system seller and community of handheld and home consoles and that it has a GOOD reputation, which is REALLY important here (which is where the Wii failed hard), i dont see it not beating the Wii.
I think Nintendo will keep it alive for long until they can make a Switch 2.0 with reasons to buy it. Nintendo said they changed their marketing campain to 1 per person from 1 per house. So we can expect a similar lifetime to a handheld which is normally around 7 years.
It will most likely peak year 3... so here are my predictions :
Year 1 : 15.2 millions --> 15.2 millions
Year 2 : 23 millions --> 38.2 millions
Year 3 : 25 millions --> 63.2 millions
Year 4 : 23 millions --> 86.2 millions
Year 5 : 20 millions --> 106.2 millions
Year 6 : 15 millions --> 121.2 millions
Year 7 : 11 millions --> 132.2 millions
Year 8 : 6 millions --> 138.2 millions
So Around 140 millions LT.
It can also change depending how it is doing in China.