Switch is doing well now, but it's final sales curve is going to look like the DS. The DS did pretty well in its first couple of years, but then it really took off to unprecedented levels. Expect to see that from Switch next year. The people who don't think the Switch will clear 80m are in for a huge surprise.
I actually agree, my prediction is 70M, I think that there won't be any Switch Pro, because the Switch is already the "Wii U Pro" of the 8th gen. Nintendo is preparing a next device which will be certainly a hybrid system as powerfull as the PS4 Pro for 2022-2023. Around 2020, there won't be anymore new third party AAA game developed for the too weak hardware of the Switch, Nintendo will keep in stable health the consolde with only Nintendo AAA games until the end, and only very few 3rd party small games. So 70-75M is my expectation.
But hey, that's fine ! 18 months ago everybody was thinking that beating the Wii U would be already a good thing. My expectation at this period was 30-35M max.
Wii U doesn't exist in Nintendo's mind, i don't think Switch being a "Wii U pro" (which doesn't make sense since the concept is literally the other way around from the Wii U) will affect Nintendo into not making a revision like they did with almost all their handhelds. I just think they will wait for the release of the PS5/Xbox and release something pretty big so it can share the spotlight.
Also, not having big third party AAA games didn't stop the Wii and DS to surpass the 100 and 150 million units. We are actually seeing more of it already on Switch so that argument is irrelevant. Games like Skyrim, Fifa 18, Octopath and Mario + Rabbis are doing really really good numbers on Switch and i don't think they will drop that market. I actually think we have seen nothing in term of third party support for Switch and that Squeenix, Ubisoft, capcom etc will have pretty big games coming in the future.
I don't think the Switch could end up performing like the 3DS while it's doing better with double the price, no deals and droughts while 3DS had a big boom in it's first year with price cut, MK7 and cie. Switch managed to surpass it without a new mario kart and no price cut with a price already higher than the 3DS BEFORE the price cut.
That leaves a huge margin of deals for the Switch in the coming years seeing how it is performing with no games and no deals. It will skyrocket during Q4 if they promote it even just a little with a small discount.