2017 was solid year for Xbox One sales in spite of exclusvies.

[Storeman67]

yvanjean said:

DonFerrari said:
Considering sales have been close to 2015 and 2016 it have been stable.

This year sales have been slowdown by imminent release of a new console by Xbox. It will be interesting to compare Xbox one 2017 and 2018 there should be a major boost in sales. 

Xbox family sales have seen a major downturn in 2017. In the UK software sales have seen a double digit reduction, while PS4 saw over 6% growth. One X demand has already stalled, and only saw any traction during launch month in the UK and US. One S is already 12 months into an end of gen downwards spiral. PS4 still has an upward trajectory, but it's the Switch that has eaten Xbox's lunch, in terms of second console ownership and mindshare.

I don't see the Xbox One family surpassing 50m lifetime.