Wanted to update this with my experience, limited to stock android 9 so far. First, I couldn't get any of the twrp or magisk updates to work. I'm pretty sure that's because of the 'system as root' situation, it seems a few update packages just don't work.
It was easy enough to verify by using adb and magisk su to view /vendor/lib/hw and look for the file that's suppose to be updated. In my case it was always the same oem date as the other files. So, after a twrp backup, decided to use a root file explorer and just change the file to the one dated april of this year (the fix).
Worked no probs. The 7.x gcam ports do seem to have better colors and detail, but that's with some pretty limited observations. Not sure about HDR 10 or anything else on 9. But the buffer fix is exactly what you'd want it to be... nice to be able to use a 7.x gcam port.
cheers