[Ultraschorsch]

From AMLogic S905x/S912 - 10bit / HDR / Dithering Testing over on the LibreELEC - AMLogic forums I would say Xiaomi are being ultra cautious about any public AML Nougat Firmware they release - especially when it has anything to do with AMLogic's implementation of 4K HDR.

Let just say they are likely in for all sorts of "fun and games" whilst bug busting if they want to properly support HDR Android Apps.

I believe there has been another two Mi Box, Nougat Beta releases come out since that first one leaked.
So its likely something will come out eventually.

If you think about it how many people are going to be buying a $69 box thinking they are going to get a bullet proof 4K HDR streamer for their expensive, shiny new 4K HDR Smart TV - which in all likelihood has 4K HDR Android streaming Apps on it anyway.

Thanks again for your answer! Ok, so I try not to flash the beta and try to be patient.