https://bugs.python.org/issue36350 / https://github.com/python/cpython/pull/12412 changed Signature.parameters and BoundArguments.arguments to be plain dicts, not OrderedDicts (for Py3.9a4).  Even though I agree for BoundArguments.arguments (in fact I argued for this behavior in https://bugs.python.org/issue23080), I think Signature.parameters should remain OrderedDicts.  Otherwise, one would get

    >>> inspect.signature(lambda x, y: None).parameters == inspect.signature(lambda y, x: None).parameters
    True

which seems plain wrong (comparing the signature objects themselves still correctly return False because __eq__ explicitly considers parameter order, but one may e.g. want to compare parameters for equality while ignoring the return annotation).