Something interesting a quote from Stacey Spears a well respected TV industry expert from spears and munsil that worked on xbox one: "On the Xbox One, 8-bit RGB is delivered to the HDMI transmitter. If you are outputting 36-bit, it is padded with zeros just before output. No actual processing is done at >8-bit. Xbox One's Blu-ray player is a matter of convenience only. A standalone Blu-ray player is better. I worked on the Xbox One, so I know the internals of the entire video pipeline."
Doesn't this pretty much confirm no dithering is used at 8bit?