FY16 - 2.74 million
FY17 - 17.79 million
FY18 - 35-38 million*
FY19 - 55-60 million*
*Predications
So since I don't expect Xbox One numbers to exceed more than 55 million lifetime, sometime before March 31st 2020, likely by December 31st 2019 since sales will likely be more than 50 million then since January, February and March 2020 won't do as significant numbers as the holiday months unless a major game drops like Animal Crossing.