I think Microsoft was caught flat footed with the release of the Pro and poor reception of the base XB1. I don't think they intended for there to be an X release
(although they should have) which is why they were a year behind. Now they are trying to play catch up. I don't think Microsoft wants to give Sony a head start, but because they just released the X, they can't release a console again in 2019. However...I think there is a huge loophole in that analysis.
I think Microsoft will release some other self contained computing product that will be fully compatible with Xbox family games. Imagine a Microsoft version of the Steam Machine except that it'd be based on Windows 10 and could play Windows and Xbox games. It'd be marketed and priced as a computer not a console even though it'd work in that role too. I can see Microsoft releasing such a computer/console in 2019 to try to steal the thunder from the PS5. Then Microsoft would follow up in 2020 with a true console release that had just enough improvements over the PS5 to overshadow it.
So here is my crazy far out prediction:
2017: XB1 X
2019: PS5 | MS Machine
2020: XBNext
2022: PS5 Pro | MS Machine 1.5
2023: XBNext X