I'm not sure it's fair to say because it hasn't happened in the 17 years of NixOS' lifespan, that it never will, when the last 5 years of NixOS have been the most active by large:
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