Is there any way to have something like a distance blur? e.g. as rays travel further you reduce the number, subsample then apply a gaussian(or algo of choice) blur across those that return, increasing in intensity as the rays angle gets coarser?

It'd be really neat to have some way of enabling really long-distance raytraced voxels so you can make planet-scale worlds look good, but as far as I'm aware noone's really nailed the technical implementation yet. A few companies and engines seem to have come up with pieces of what might end up being a final puzzle, but not seen anything close to a complete solution yet.