I think we can stick to the DisplayHDR certification as a "HDR standard" reference, since future displays are likely going to be certified with it, at least on the consumer end, where it concerns the Mini used as an HTPC.
But my above question on the OS itself is more on the editing / color grading prospects. I remember back during the Cheese Grater Mac Pro days, still on OS X 10.6.8 and FCP7, since the OS itself does not support 10-bit, we had to install a BlackMagic Intensity Pro, which is just a 2 lane PCI card that takes care of 10-bit 4:2:2 HDMI, where we connected a SONY PVM OLED to it. The monitor could only get inputs from "supported" applications, it could not act as a regular display recognized by the OS and used as a mirror / extend desktop for instance, therefore the usefulness of such a setup was not that great.
If the Mini's limitation is just on its built-in I/O, then we can hope a TB3/USB-C external video card can deal with this. If it is OS or firmware level limit then it is dead end, for now.