They could also potentially sidestep the issue by designing a discrete DisplayPort to HDMI chip into the system, so the HDMI 2.1+ implementation is firewalled from the open source stack. Maybe next time, if the HDMI Forum still hasn't budged by then.
Yeah, the chip they used isn't ideal though because it converts DP1.4 (32Gbit) to HDMI 2.1 (48Gbit), so the bandwidth is bottlenecked on the input side. Ideally you'd want a chip which takes DP2.1, which I'm not sure exists yet, and the upcoming Steam Machine only supports DP1.4 so it wouldn't have helped in that case anyway.
