Damn, that's impressive. Didn't know his work.

I completely agree with you that this is more of a custom denoiser problem. I don't know if you are aware of pixel art upsampling techniques, like hq2x. If I were to try to improve this guy artwork, I would try to reverse engineer hq2x as a downsampling algorithm and use it to downscale his 3d renderings to a more stable pixel art,