

If you want it to still be steam OS and compatible with games then you couldn’t use kernel.org kernels that’s the point.
If a person stands to make a lot of money figuring out how to use a regular, non-anticheat kernel then they will do it. It would be a lot less difficult to do when the kernel code is open source.
For anti-cheats, it isn’t the case, as with Windows, where you can semi-trust that the kernel isn’t lying. If an anti-cheat runs and wants to see what DMA devices are connected it uses the kernel to do that and it trusts that the kernel isn’t lying. You could trivially modify the Linux kernel’s source code to not list a specific card when asked by a kernel module.
That’s great, it beats having to buy new hardware!