Ray tracing is huge for geometry, you can fill the entire video memory with geometry data, like a huge detailed landscape or car, anything non-deformable, without much impact on performance. Foveated rendering also has a massive impact on ray tracing, you just ray trace at a lower sample rate where you're not looking, then blend the samples together with contrast adjustment.

Keep in mind the impact Tobii is showing is for low resolution VR, the load will be reduced significantly further when the screen allows for a greater disparity between central and peripheral PPD, like on the Pimax 8KX (3K equivalent per eye), future headsets at 6K or so should see 80% reduction, the total ray traced resolution across both eyes should top out around 1600p with anti-aliasing.