My 2 cents on this.
I have been forcing ‘444,10bit’ into /sys/class/amhdmitx/amhdmitx0/attr (set in /etc/rc.local) since May 2018 and all my HDR files (demos and movies) have been working fine on my 65C8.
Now I just installed the october update.
I can’t find the “Enable HDR autoswitching” any more.
Forcing ‘444,10bit’ seems to still be working (at least echoing /sys/class/amhdmitx/amhdmitx0/attr provides me wit the expected output).
I tested plenty HDR files. All are still working.