I've seen some people say that since HDMI 2.2 recently released the HDMI forum doesn't care as much about "protecting" 2.1 anymore.
If FOSS drivers support HDMI 2.2 when devices start shipping with HDMI 2.2 ports then this'll be disproven, but the HDMI forum held off on allowing AMD to implement 2.1 support in their Linux drivers for years and only relented when they released HDMI 2.2. Valve with the Gabecube probably didn't have much to do with it considering how low volume it is.
If FOSS drivers support HDMI 2.2 when devices start shipping with HDMI 2.2 ports then this'll be disproven, but the HDMI forum held off on allowing AMD to implement 2.1 support in their Linux drivers for years and only relented when they released HDMI 2.2. Valve with the Gabecube probably didn't have much to do with it considering how low volume it is.