I will try to give my 2 cents. As you correctly state, Cython is in effect another language.

Now, a core principle in the design of Cython is to be as much as possible source compatible with Python, which is a language without static types. This is not a very good principle for me - I would rather work in a language that is not literally identical to Python, but has its own design. Adding static types often requires to do things slightly differently. In Nim a find a very principled and well designed language, and PyMod seems a great to tool to make interoperability with Python easy.