IMO the absence of a `--pure` flag (the `-i` flag seems not to work in the same way) makes `nix develop` an unsuitable replacement for `nix-shell`. A few SO threads and nixpkgs issues seem to agree, but if I'm misunderstanding I'd love to learn more.
To be clear, nix-shell --pure serves this use case by accident; it basically drops you into the shell with generic-builder.sh sourced and the build environment for a Nix derivation. This is useful for debugging Nix derivations, and if you are using mkShell you can minimize the pollution, but it's not exactly a development environment tailored for the typical software-engineering workflow.
The tool that (ab)uses nix-shell/nix shell to get this right is devshell [1], which creates an activation script (similar to NixOS itself) that provides a real reproducible development env which works with shells other than bash.
