It is strange that you characterize Cython as a limited sub-language. Cython supports almost the full Python language, plus adding a superset for producing native C code. In addition, Cython can be used to wrap C code, so what you describe as "exportpy" is possible as well. Cython is a mature project, being in use in various parts of the scientific python ecosystems such as in Pandas and scikit-learn. Nim sure looks interesting but from what I hear, the language and the compiler still have rough edges. In terms of stability, maturity, and ecosystem, I'd say Cython has a clear advantage.