Is it worth to emit more specific (but possible uniform) error messages in other unpacking cases (see msg307999)?

FYI if a class implements __iter__ which returns non-iterable, the following error is raised:

>>> class C:
...     def __iter__(self):
...         return 1
... 
>>> a, b = C()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: iter() returned non-iterator of type 'int'