When looking at cleaning up video noise, have you seen Gleb's experiment using ebsynth? At the end of his video he uses one clean cycles render and uses ebsynth to apply that to a checkerboard textured animation.
I have tried it, but not for denoising purposes! What a cool idea. I found that it was a little wobbly in my tests, but with enough keyframes and Gleb's idea of using a grid texture to help the mapping, it could work. I wonder if in the future we'd only need to render out every X keyframe and let a neural network do the rest 🤔