I would actually be very surprised if Microsoft decided to release another iteration of the Xbox One, especially in the near future. I like my Xbox One and use it quite often but I've not had the desire to upgrade it. Maybe once my OG model kicks the bucket I may as well get the more powerful version but even at this point it seems like these half generation upgrades are splitting the fan base.
Honestly it's the old version of the console that's holding the X back and I think when Microsoft does decide to release their next thing it needs to be a true next gen or they need to change course and focus completely on PC. Or maybe they just need to make a more gaming focused PC OS instead of hardware.