Wouldn't that be an application (or at most system library) concern though? The OS is just there to sling pixels, it wouldn't have any idea whether those pixels are blurry… well for VR it would all be OpenGL or equivalent so the OS just did hardware access permissions.

I think the context is that foveated rendering ties sensor input (measuring gaze direction) to the rendering pipeline in a way that requires very low latency. Past a certain point reducing latency requires optimizations that break normal abstractions made by user land, so you end up with something more custom. I'm not sure why that would require a whole new OS, the obvious path would be to put the latency-sensitive code onto dedicated hardware and leave the rest managed by Linux. If a bunch of smart people thought XROS was a good idea there's probably something there though, even if it didn't pan out.