We also had a similar use case, so I built Snex[0] - specifically for Elixir-Python interop. Elixir-side spawns interpreters with Ports managed by GenServers, Python-side has a thin asyncio runtime to run arbitrary user code. Declarative environments (uv), optimized serde with language-specific objects (like `%MapSet{}` <-> `set`), etc. Interpreters are meant to be long lived, so you pay for initialization once.

It's a very different approach than ex_cmd, as it's not really focused on the "streaming data" use case. Mine is a very command/reply oriented approach, though the commands can flow both ways (calling BEAM modules from Python). The assumption is that big data is passed around out of band; I may have to revisit that.

[0]: https://github.com/kzemek/snex