There seem to be some action items from this thread that I haven't seen reflected in the PEP source code yet.
- Change the title (I like "Core support for typing module and generic types" but maybe it can be shortened to "Core support for generics in the typing module" -- if you like that, go for it)
- Change __subclass_base__ to __mro_entry__
types.resolve_bases and related changes
- Maybe some clarifications summarizing the feedback from this thread (esp. Nick's)?