> Most people don't have hardware that requires HDMI 2.1 in order to get full use out of them, and of those who do, not all of them use Linux and/or care about open source drivers.

Arguably true, but I think that is changing all the time while there is a push towards open-source drivers regardless of the average user knowing/caring what that is, along with resolutions and refresh rates increasing.

I was affected by HDMI Forum's decision by buying an off-the-shelf 4K 120Hz monitor which refused to work at that resolution/refresh rate on an HDMI cable.

I was not expecting an arbitrary decision affecting software to be the cause instead of a hardware problem - which took me a while to figure out.

Now I know if I want to use my hardware to the full capacity, I need DisplayPort in future.