3.7 (or maybe even 3.8) support will start as soon as we can have a "final" 3.6 - which might be couple months from now. I think 3.7 won't be done in 2019, unless some magic source of funding pops up.
3.7 it's a minor update from 3.6, that basically consists in changes to the standard library rather than the language, and 3.8 I think it will be the same, so once the 3.6 support is implemented it will take less time to implement 3.7 support.
Dataclasses are a sweet feature that I can see getting wide adoption pretty quickly. This said, they have a backport and it's mostly just sugar, so I expect one could probably get them working on 3.6 pypy.
The main way big corpos are sponsoring os is hiring the developers typically. That comes with a whole lot of things that some people don't want to deal with, like changing your place of residence
I doubt that they allow you to work on a VM there. I saw only marketing and content jobs there. In Munich or Zurich they do have VM teams. Maciej is from Warsaw, he could do surfing in Munich. Armin Rigo is in Switzerland.
How realistic is it for an experienced programmer to dedicate 4 hours a week and join as a contributor? Not sure it is enough to bootstrap enough "project" domain experience to be productive. Asking for a friend.
There are some “easy” tasks to achieve 3.6 full compatibility, tell your friend to try it and see. We are around on #pypy on IRC, mostly european timezones