You think so?. XBO seems to have sold around 6'5M in 2018. If XBO sells, let's say, 5M in 2019, it will need 4M before next XBOX launch in 2020 (all of this if next XBO launch in 2020 and not in 2019).
I really think it won't reach 50M before that.
9 million in nearly two years? I see it happening.