I think the first step is probably to get consensus on whether this is desirable or not.  That might require a trip to python-idea, or it might not :)

As for the patch itself, you should definitely *not* include any changes other than the ones you are proposing.  Otherwise reviewing the patch is very difficult.

As Ezio said, as a new feature this could only go into 3.4, so the patch should be against the default branch in the mercurial repository.