What's holding swift is not having a good story to call a swift compiled extension from Python/JS/Ruby/PHP.
Python's community is huge, very active, Python is everywhere, and it needs compiled extensions. And tooling to make them BFF, like pyo3 and maturin, is great
And that's how we got cryptography, pydantic core, polar... Which motives even tooling to be written in rust as a side effect, and how we have uv and ruff.
The scripting community is the most active, if you got them on your side, you get access to a huge pool of devs.