Something like this experiment I had laying around?
It might need some work to integrate with the nixos.org website, and the fork (sorry can’t share right now) is extremely WIP and needs some cleanup. (Just now I rebased it on top of the current nixpkgs.)
If the community, and those in charge of the website, are interested in getting this up and running, then I’ll continue fixing this up, except acquiring feedback from the community, I think the interface is close to being just right.