Not sure if this answers your question, but the lack of (real) threads in Python is a big blocker if you are running any kind of performance-related code, e.g. a back-end. Yes, you can kinda emulate threads with processes, but suddenly, your code becomes much more complicated and all the readability benefits of using Python disappear.

For a very long time, OCaml had the same problem. Now that OCaml has finally entered the multicore era, I will see if I can get back in touch with the OCaml magic :)