Also, there are some large recent initiatives to improve Nix and NixOS, such as Flakes (which give Nix package sets a standard layout and improves hermatic evaluation). Eelco Dolstra has also presented a proposal at NixCon 2020 to improve the module system's usability:

https://www.youtube.com/watch?v=7sQa04olUA0&t=1h24m18s