Thanks for bringing me in. The PoC implementation looks nice. Whether I'd like to support this in Cython? Absolutely. Requires some work, though, since Cython still doesn't implement PEP 489. But it shouldn't be hard, if I remember the discussions from back then correctly. I could try to free some time in August to catch up with this. That would still fit into the pre-alpha phase of Py3.7.

Unless, obviously, others would like to give it a try in the meantime. It's mostly about splitting up the current generated module init function into separate phases. Ok, there could be some minor obstacles along the way. ;)

I created a ticket for it in our own tracker for now.
https://github.com/cython/cython/issues/1715