It seems like very few pepople are testing Python 3.8 so far. I'm making this assumption because many projects using Cython cannot be installed on Python 3.8 and I didn't see much complain so far.

My Python Maintenance team at Red Hat is working on fixing all the stuff for Python 3.8, and we are the most exposed by such backward incompatible change. FYI we modified a few Fedora packages to explicitly run Cython as part of the build to ensure that C files are always regenerated with Cython. So if PyCode_New() API change again in beta2 but Cython takes that into account, Fedora Rawhide will be unaffected.

Note: we are not sure yet if Fedora 31 will be able to switch to Python 3.8 by default, the build of many package is still failing, for various reasons (sadly, this change is far from being the only reason!).

More info:
https://twitter.com/VictorStinner/status/1138067403341012997