I found the stray patch cum bad commit that broke hardware decode .. so the next nightly that's build (scheduled for 5th Jan AM GMT) will have working hardware decode again. Impatient users can grab something from https://chewitt.libreelec.tv/testing/ .. there are no functional improvements so GXBB/GXL/GXM are working nicely and newer devices still have some issues, but that's an improvement on black screens and no video everywhere.
NB: I have added a possible workaround (not fix, workaround) for borked USB ports on Odroid C2 and the meson-gxl-s905x-p212 device-tree may now have working BT/WiFi .. I'm still not near my usual test devices so you'll have to test for me.
Happy New Year!