The fact that NSMBUDX sold 3mil is pretty amazing! See what a Mario port can do!
3D World should be the next one.

Errr ... what? Smash already outsold Smash Brawl for the best selling title in the series and will cruise past Odyssey and Zelda LTD soon enough. It's also already the top selling fighting game (any franchise) in the history of video games. 

Expected 14.5-15M. 

Then you should have said "It sold well but I expected more"  because those numbers are definetly not underwhelming. 

Te way it's selling NSMBUD could reach it, too. Unless SMM2 cuts off it's legs in June. In any case, one of both certainly will also reach that mark.

And it all disappears come 2020.

A-mazing! The Switch is already close to 35 million.

I wonder what BotW LT will be, could be 15 million. Also, where can I find Xenoblade 2 numbers?

So the Q3 forecast for this quarter (Q4) was 1.7m HW for Switch, and it did 2.5m I think.

SW forecast for Switch was 11m and it did ~24m.

So after downgrading their forecast, they did quite well against their lower forecasts.

Overall about 17.5m a year. That would average to close to ~90m in 5 years.

Nowhere, we only know that it reached 1.53m units as of september 2018. Nintendo only provides sales of the 10 most selling games in the quarter and LT

Why should it? Next gen consoles?

As long as PS4/XBO will get support from 3rd party publishers, Switch will also, as they will certainly get one and the same version starting 2021 to save money.