The problem with asyncio is that you can't take advantage of both it and the bazillion synchronous-io libraries already in the ecosystem.

For large web apps it's still pretty much a nonstarter unless you want to not be able to take full advantage of libraries like sqlalchemy.

Nodejs had a great advantage by starting with asyncio from the beginning.

M:N threading would have been a much better fit, though that's out of question given the GIL.