But is it hard getting packages into the Nix ecosystem? If there's too much friction or if it's too hard to resolve all the dependencies yourself before pushing your pkg, I fear it may suffer from lagging behind the latest available versions of most packages.
Everyone has to resolve their immediate dependencies anyway to push it to pip or whatever else, or nobody can install it. The only additional dependency to push it to Nix would be the language interpreter.
Nix doesn't require you to specify the entire dependency tree; each dependency specifies its own dependencies, and those are resolved during the build process.
(For the record, at least Haskell, Python, and node.js packages are pulled into the nixpkgs tree from their respective package repositories regularly, albeit many missing native dependencies; there's a separate file that you can edit and send a pull request for packages which have native dependencies.)
