With the current rate (averaging last 12 months), the date is 21st of November 2020 or 102 weeks from the latest figures. Based on my calculations, both of them should reach 55 million mark by that time. But I'm pretty sure that XB sales will diminish with time, so if the Switch stays at the same level, we should see it outselling XB1 no later than in Q2 2020 (that's with the 30% decrease in XB1 sales).
Edit: For those who predicted that it's going to happen before 2020, Switch in 2019 would have to start outselling XB1 with the ratio of over 4:1. Personally I don't think it's going to happen, but who knows.Last edited by Kristof81 - on 06 January 2019