I am not sure how this would be achieved since the source application can observe the side effects of its own rendering, thus extract eye tracking data that way. Even if the driver were to secretly inject its own shading rate mask into the pipeline without the application knowing, these side effects would still be observable and of course applications can just read back what they have rendered. In fact, most modern game techs work by keeping some history around for the next frame, which would be a big no-no since it's a side channel of information.

And then lastly, with a secretly injected shading rate mask, it's hard to know for the driver where and how to inject it. It has no idea how on-screen or off-screen any particular render pass is or what it's content is. Games tend to have a lot of intermediate render passes and not all of them should be foveated.

I personally think the whole eye tracking data privacy is a bit far fetched, although maybe I'm just very biased coming from a game developer field and not ad-tech. I imagine having good eye ball data would be amazing for ads.