[...]
Agreed. I'm currently thinking that I need to do what several people
have suggested and break this into two completely separate PEPs:

1) Sublocal namespacing
2) Assignment expressions

Sublocal names can be used in a number of ways. There could be a "with
sublocal EXPR as NAME:" syntax that actually disposes of the name
binding at the end of the block, and "except Exception as e:" could
shadow rather than unbinding. Maybe list comprehensions could change,
too - instead of creating a function, they just create a sublocal
scope.

That may be the best way forward. I'm not sure.

ChrisA