I'll keep shouting from the sidelines, if it's ok.

Is the following behavior still desired

>>> [z := x for x in 'foo']  # valid

over forcing parentheses here as well?

>>> [(z := x) for x in 'foo']  # also valid, but redundant parentheses

The section on when to add parentheses in comprehensions would be a lot simpler if the answer was 'always', with an asterisk saying that the restriction might be lifted for some cases if there is a demand and a good-enough implementation.