I've have the XT-4 and now the XT-5. Here are my observations when using these cameras for astrophotography:
1. Crop sensor - First, a crop sensor gives you more "magnification" than a full frame sensor, and that can be actually useful in most circumstances. Second, the noise level in the backside illuminated X-trans sensor remains well controlled through the typical ISOs needed for astrophotography. Besides, most images are created by stacking many images, which helps reduce the effect of high ISO noise.
2. Screen position - Having used the "flippy" screen on the XT-4, I found the screen gets in the way more often than not, especially when I use an L-bracket. I find the multi-positional screen on the XT-5 way more versatile, even with the camera pointing straight up. If you want flippy, you can always get the XT-4 or the H2, and flip away.
3. X-trans sensor benefits - One benefit that most reviewers miss is that the X-trans sensor can pick up more of the near-IR area of the spectrum, allowing you to capture more detail of nebulae than typical Bayer sensors. Also, the X-trans sensors don't need a detail-robbing low-pass filter that Bayer sensors need to mitigate moisaicing. The only down-side to X-trans images is that Lightroom doesn't do a good job and de-moisaicing the RAW image. But you can get DXO's RawPrime 2 to demosaic the images properly. (Note - As of this time, DXO has not released a version of RawPrime that handles XT-5 RAW images.)
4. Dials - Sure, you can't read the dial settings in the dark, but you can read the screen, which shows you the settings as you adjust the dials. If you can't find the dials at all, then you have bigger problems than being able to read the settings. I'd rather have dial settings than PASM dials and complicated menus when it comes to adjusting a camera in the dark. Also, you can create a Q custom setting that gets you most of the way there for your typical astrophotography settings.