For Livebook, this looks really cool. Love that it calls CPython directly via C++ NIFS in Elixir and returns Elixir-native data structures. That's a lot cleaner than interacting with Python in Elixir via Ports, which is essentially executing a `python` command under the hood.
For production servers, Pythonx is a bit more risky (and the developers aren't claiming it's the right tool for this use case). Because it's running on the same OS process as your Elixir app, you bypass the failure recovery that makes an Elixir/BEAM application so powerful.
Normally, an Elixir app has a supervision tree that can gracefully handle failures of its own BEAM processes (an internal concurrency unit -- kind like a synthetic OS process) and keep the rest of the app's processes running. That's one of the big selling points of languages like Elixir, Erlang, and Gleam that build upon the BEAM architecture.
Because it uses NIFs (natively-implemented functions), an unhandled exception in Pythonx would take down your whole OS process along with all other BEAM processes, making your supervision tree a bit worthless in that regard.
There are cases when NIFs are super helpful (for instance, Rustler is a popular NIF wrapper for Rust in Elixir), but you have to architect around the fact that it could take down the whole app. Using Ports (Erlang and Elixir's long-standing external execution handler) to run other native code like Python or Rust is less risky in this respect because the non-Elixir code it's still running in a separate OS process.