Nice idea indeed, thanks for the patch.

For the doc section, I’d prefer to de-emplasize the specific use case of **kwargs, in favor of mentioning dict conversion in a general way:

  Converting the namespace to a dict
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  
  Namespace objects are iterable so you can easily convert them to a
  :class:`dict`::

     args = parser.parse_args()
     argdict = dict(args)

  This makes it easy to introspect the namespace or to pass the
  command-line arguments to a function taking a bunch of keyword
  arguments::

     somefunction(**dict(parser.parse_args()))

 
+    def __iter__(self):
+        return iter(self.__dict__.items())
Isn’t “return self.__dict__.items()” sufficient in 3.x?


Alternate idea: don’t implement __iter__, which is sorta too broad, and implement a method that just returns a dict.

Musing: Isn’t Namespace (technically: _AttributeHolder) very much like a named tuple?  Could some code be removed by using named tuples in argparse?  Note that named tuples provide a method to convert themselves to a dict, and are efficient (IIRC).