> Me, I wait for Python 5 (=2+3) which will be able to import Python 2 modules, so that you can gradually convert your code to the newer version.

Thank you for saying this! For those interested in this direction, there was a discussion about it on HN a couple of months ago:

https://news.ycombinator.com/item?id=10823406

Proof-of-concept examples embedding Python interpreters within themselves:

https://gist.github.com/dutc/eba9b2f7980f400f6287

https://gist.github.com/dutc/2866d969d5e9209d501a