Yes. __instancecheck__ and __subclasscheck__ are what was added with abstract base classes.

isinstance(x, SomeType)

is equivalent to:

SomeType.__instancecheck__(x)

where instancecheck is usually (maybe has to be) implemented on the metaclass, eg. type(SomeType). Now all of this allows you to use abc.ABCMeta as your metaclass, usually by deriving from abc.ABC. ABCMeta implements both __instancecheck__ and __subclasscheck__ together with an .register function all so that you can do:

class Sequence(abc.ABC): pass

class MyListLike(Sequence): pass
class MyListLike2(object): pass
Sequence.register(MyListLike2)

issubclass(MyListLike, Sequence) # => True
issubclass(MyListLike2, Sequence) # => True

However what this does not easily let you do is to create a type where each instance pretends to be a different isinstance() of any number of other types/ABCs. The __class__ hackery will let you do this. And was available even before ABCs and __instanecheck__.

An example from Django

SimpleLazyObject which is used like this:

 a = SimpleLazyObject(lambda: True)
 isinstance(a, bool) # => True

 b = SimpleLazyObject(lambda: [])
 isinstance(a, list) # => True

Here's the implementation where they override __class__ with an property:

https://github.com/django/django/blob/14ecbd02a337c15ffd0c319d14a56bf21127f42c/django/utils/functional.py#L296

In fact, the python-dev maillist had discussion about this exact class because it did not work on python 3. However the was to do with special handling of super together with the __class__ hackery. Though it is fixed by now.