It is a win win situation, they get to write a new blog post about doing a Python to Rust rewrite.

Unfixable errors? Why unfixable? Python is Turing complete. I can see difficult to fix, but not unfixable. LLMs lower the bar to refactoring code mistakes.

What would be your goto for the ML training pipeline?

I have the impression that Python basically wins by default in those spaces due to the lack of many good libraries in other languages (except for, like, C++).

But curious if this is just a very outdated view of the world

Yeah Python seems like a bad choice. LLMs seem to write low quality Python compared to Rust, presumably because there is a lot more low quality Python in their training sets than there is for Rust.