Foveated 3D Graphics (2012) [pdf]
research.microsoft.com
research.microsoft.com
The excellent http://www.adriancourreges.com/blog/2015/11/02/gta-v-graphic... shows how many pixels are written to to construct a scene using rasterization. Many many intermediate render targets are involved. Any intermediate layers that are not directly in screen-space would not benefit from foveation.
Raytracing/ray marching etc. working on a pixel by pixel basis would be far more suited to larger fuzzy pixels where you are not looking.