+0 I think this is with worth considering.  Whenever the use case arises, the workaround is awkward.  Code would be clearer if assignment expressions were liberalized to allow unpacking.

The PEP aspired to avoid complex lvalues that might be hard to read or that had tricky semantics.  Unpacking is one the simpler cases and would be mostly harmless and sometimes beneficial (and not just for the uncommon case of wanting simultaneous assignment).