Yes, there were various attempts to do this in the container ecosystem, but there is a hard limit on layers on Docker images (because there are hard limits on overlay mounts; you don't really need to overlay all the Nix store mounts of course as they have different paths but the code is for teh geenral case). So then there were various ways of bundling sets of packages into layers, but just managing it directly through Nix store is much simpler.