No, the workaround was for duplicating the existing behavior if the fix (raising an error like a normal dict does) broken someone's code. The *only* possibility here is to have a __reversed__ that raises a TypeError.
What is it that makes reversed raise a typeerror on dict here? Not that we can change it at this point, but reversed blindly using len and __getitem__ for user classes but not on dict is rather inconsistent. I suppose the dict TypeError special case catches common mistakes? In which case adding a __reversed__ that raises a TypeError to Mapping seems to make sense for the same reason.