Firstly, how long do you expect the Wii U to be around, if it will sell only 40 million in it's lifetime.
I expect the Wii U to be sold until at least 2020, in that time it will easily beat 40 million. However, it is not likely to beat the Wii's 96 million sold but it will beat the NES (2nd best selling Nintendo home console) sales at 60 million at least
Xbox One, PS4 and Switch (+ Many Retro Consoles)
'When the people are being beaten with a stick, they are not much happier if it is called the people's stick'- Mikhail Bakunin
Prediction: Switch will sell better than Wii U Lifetime Sales by Jan 1st 2018