On the other side, we observe more and more inter-languages's ecosystem crossing from/to Python to leverage its gigantic set of libraries. Julia interface with a lot of other languages but it is a big trend for the last years.

I think the two-language problem begins to be as we move forward a network of multi-languages calling each other instead of either having to rewrite everything from scratch either relying on a C/C++/Fortran/Rust lib and the C ABI to patch them. We may finish with a set of "meta"-langurust in C code nameages permitting the interaction of a large number of libraries and programming languages outside of their silo.

Moreover Julia coupled with Pycall could "corrode" à la Rust for a more smooth migration to pure Julia.