I think its mere existence and influence is already good enough. A fair number of modern open source projects either come with Nix flakes or are designed to work well in an immutable environment whether it is NixOS, SteamOS, or inside of a Flatpak or Docker container. The Nix contribution is trying to convince things to 1. stop hard-depending on FHS, 2. allow things to build and be used in a hermetic way, i.e. pushing projects to stop fetching things from the internet during the build phase or at least provide an escape hatch to avoid this.

If it hasn't been working, they could've fooled me. Nixpkgs definitely appears to be the largest and most up-to-date single Linux package repository out there.