we have already overloaded '+=' to map to left.operator_add(right). But there's no reassignment involved, which would be a bit error prone, in combination with operator overloading.
I can imagine adding the operators like this :
a -= b | a.operator_minusEquals(b)
a *= b | a.operator_starEquals(b)
a /= b | a.operator_slashEquals(b)
But then they wouldn't do what you are looking for.
Maybe we could annotate the operator-method with something that indicates that the result should be assigned to the feature call on the left.
Please file a bugzilla to track further discussion.