It would be counter productive to take all that FR reduced pixel data on the GPU and then resample it to fill the native panel while still on the GPU. You move that process to the HMD chip and thus data bandwidth is vastly reduced too. This is why FR is tooted for mobile / portable devices as it has an improvement on battery life due to reduced bandwidth (power) demands.
That is what I read anyway.
If you search for "Foveated rendering bandwidth" there are many articles making this claim.
Look at this article:
Find the heading "Foveated Transmission" for a visual representation of how that works.
As for the 8K-X, lets hope that the driver for the HMD can recognize a foveated frame vs a full frame and a software/firmware patch will be built to process it as the technology matures.