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.
https://blog.pyston.org/2017/01/31/pyston-0-6-1-released-and...
https://opensource.googleblog.com/2017/01/grumpy-go-running-...