I think the obsession with the GIL is sort of missing the point - people on python2 live with the GIL and don't really miss it, I don't think that's really the killer feature to drive python3 adoption. Especially considering its almost impossible to do without breaking something (most likely C extensions) and when you see the wailing and gnashing of teeth that came from python3 forcing people to fix their text encodings it doesn't look seem like more breaking changes are going to drive python3 further. What's more, python already has quite convenient multiprocessing, and python3 concurrent.futures makes it even easier - frankly I think too many people complain about the GIL without having tried multiprocessing (doesn't help that it seems every tutorial starts with multithreading, then tells you it doesn't really work, and only then tells you about multiprocessing). You only get to complain if that doesn't work for you!

Personally I think the driver is going to turn out to be type annotations. When you see the enthusiasm for adding type annotations to JS (typescript, ES6, etc) its easy to see that translating to python. Static analyzers can be a huge help (you can already get a taste of it with PyCharm) and I for one would like to move away from "traceback driven development" where you just have to keep re-running the code until all the preventable glitches are worked out...