In test/test_multiprocessing.py:
"""
   def test_waitfor(self):
       [...]
       with cond:
           result = cond.wait_for(lambda : state.value==0)
           self.assertTrue(result)
           self.assertEqual(state.value, 0)
           for i in range(4):
               time.sleep(0.01)
               with cond:
                   state.value += 1
                   cond.notify()
"""

Shouldn't the `for` loop be outside the outer `with` block?

In Lib/multiprocessing/managers.py:
Is there a good reason why the wait_for() proxy method can't simply be implemented as:
return self._callmethod('wait_for', (predicate, timeout))?

(There may be, I just didn't check).

Finally, the documentation should be updated (Doc/library/multiprocessing.rst).

Otherwise, it would probably be better if you could submit a contributor agreement (and also maybe update your name on the tracker), unless that's a problem for you?