Looks like there's stilllots oftest_typing failures if I apply this diff to your PR branch:

diff --git a/Lib/typing.py b/Lib/typing.pyindex 8c874797d2..8caeb915d8 100644--- a/Lib/typing.py+++ b/Lib/typing.py@@ -1733,7 +1733,7 @@ def _allow_reckless_class_checks(depth=3):     The abc and functools modules indiscriminately call isinstance() and     issubclass() on the whole MRO of a user class, which may contain protocols.     """-    return _caller(depth) in {'abc', 'functools', None}+    return _caller(depth) in {'functools', None}

The trouble is that these__subclasscheck__ calls call into_ProtocolMeta.__subclasscheck__, which might raise:

But we don't want it to raise if the__subclasscheck__ call is coming from an__instancecheck__ call.

Ultimately, it does sort of feel liketyping is the module that's "in the wrong" here. Theabc module makes the assumption thatissubclass() calls will never raise, providing both arguments are instances oftype. That's true for the vast majority of classes, so I think it's a reasonable assumption to make.typing is the module that's doing a surprising/unusual thing here, so it seems reasonable to say that it'styping that should have to do the awkward workaround. It's unfortunate how fragile that makes some of the code intyping.py, but I thinkPEP-544's semantics are too well-established now to change the behaviour.

I feel like this change isn't worth the churn.