Can this be done?
No idea if the Cython .so extension can be dynamic loaded from a php script or does it needs any extra manage?
The short answer is no. Cython extensions use the Python C API, so they can't be loaded and called directly from PHP. They will typically take and return PyObject structs as arguments (Python objects). You'll need a Python <-> PHP binding to load the .so and do object conversion.
Use a Cython extension from a compiled python in php?