on these atomic distros where even something like syncthing involves shenanigans to keep active week to week? Ain’t happening.

I don’t see why you couldn’t kexec into a new kernel. kexec will load a kernel into memory from an already running kernel, and jump into it. It’ll suck for the user as they’ll have to semi-reboot everytime they want HDMI 2.1, but it’s easy and doesn’t install anything.

There’s also live patching, but I think that’ll be a bit of work.

Of course the kernel needs to be compiled with those options enabled, but most distros do.

Edit: And they probably won’t work with kernel lockdown/secure boot.

DP has an option to transmit HDMI signals instead, this is what passive adapters use and will still have the same HDMI 2.0 issue. A DP source can be passively adapted to HDMI, but a HDMI source cannot be passively adapted to DP.

You can also get active HDMI adapters which actively convert the signal, and can work with HDMI 2.1. Intel actually has an active converter chip built into their ARC GPUs, and is how they get around this issue.