Panasonic TH-55EZ950U OLED TV and a Yamaha YAS-107 soundbar, both of which support HDMI 2.0a.
I also tried playing the same 10-bit file with the soundbar out of the loop, ie a direct Vero 4K > TV connection. Same result. TV reports 8-bit signal. Log for this here; https://paste.osmc.tv/xusixuwonu
The odd thing is the TV does report a 10-bit signal, with no banding being present, when forced by enabling 444,10bit in rc.local