Piracy being easier is the only risk. Once again ruining the experience of legitimate customers to try and stop a thing that they have had no success at even slowing down.

The security of mega Corp IP.

HDMI 2.1cspecs are closed source.

Having to use systems that swing to more closed solutions is going to degrade security in more places.

First thing I could think of is taking advantage of the ARC to spy on you.