I'd say there are two remaining roadblocks. First and biggest is kernel level anti-cheat frameworks as you point out. But there's also no open source HDMI 2.1 implementation allowed by the HDMI cartel so people like me with an AMD card max out at 4K60 even for open source games like Visual Pinball (unless you count an adapter with hacked firmware between the card and the display). NVidia and Intel get away with it because they implement the functionality in their closed source blobs.