Ideally, augmented assignments would also become "rebinding". However, this may have compatibility problems.
Unfortunately yes. It might have been better to define them that way in the first place, but changing them now is dubious.
I'm not so sure. You need an existing binding before an augmented assignment will work, so I don't think there can be any correct existing usages that would be broken by this.
Indeed. If x is neither local not declared global, x+=... is always an error, even if an x at an intermediate level exists, so THAT shouldn't be used as an argument against this.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)