Currently, some type checkers rightly complain that a method is decorated with abc.abstractmethod when the class's type does not inherit from ABCMeta.  Adding a metaclass is a fairly heavy dependency since you're forced to poison all of your other metaclasses with the same base metaclass.  It also brings in possibly unwanted type registration that ABC comes with.

Now that abstractmethod's usage is extremely well-understood, would it make sense to move the checking logic out of ABCMeta?

It could either be put into object so that no base class is necessary (at the cost of slightly slower class creation), or else in a non-meta base class (say, HasAbstractMethods) now that __init_subclass__ is in all extant versions of Python.  Inheriting from such a non-meta base class would avoid the poisoning problem described above.

As far as I can tell, neither solution breaks code.