I am not sure what you mean by "properly concurrent", but I am guessing that you are referring to the fact that Python code cannot use more than one core becaus

I am not sure what you mean by "properly concurrent", but I am guessing that you are referring to the fact that Python code cannot use more than one core because of the GIL. This limitation also applies to Twisted applications. For high volume apps, it often makes sense to run multiple instances of the app behind a reverse proxy. That's the only way to make full use the CPU when running Python. What is "socket lockup"? The word "lockup" is nowhere to be found on the page you references.