> Years ago it was a lack of any support for shells other than bash and zsh. I've been using fish for over a decade.

It used to be that running `nix-shell --package` would drop you into bash. With the newer nix command equivalent, `nix shell` retains the same SHELL.

When writing Nix packages, practically the only supported shell is bash. But, that's less of an issue, since it doesn't affect what interactive shell you use.