Never?  4 years or less? Perhaps, 5 or more? How long will it take for N.Switch( and potential upgrade for the "switch" family) exceed the X1S and X1X sales.

3-4 years is what I'll say. I'm starting to see around 50-60 million lifetime to likely be the best that the Xbox One will end up with.

10 mil 2017
15 mil 2018
18 mil 2019

Xbox One is about 30 million now, I don't think it can do 5 million per year for 2018 and 2019.

Within three years.

If ninty keeps rolling like it currently does, 2 years
Otherwise 3

Thanks for participanting. Alson, i just add a pool.
One more thing, Sorry for my english, feel free to correct me if necessary.

Two-three years should be enough, specially if they manage to solve the hardware droughts before Animal Crossing and Pokemon.

Mid to late 2019.

4yrs is reasonable

With the hardware we know about, or is currently on the market, I think it will be 4 years. If Nintendo does a revision, and releases a 4G Switch/Switch Phone in 2019, I could see it happening in by the end of the year, or less than two full years.

4 Years ...