[I'm responding to myself here...]
On Tue, Jun 28, 2022 at 4:44 PM Jukka Lehtosalo
... Finally, have you asked for feedback from some more typical users of typing (that are not active on typing-sig and don't work on type checkers)? In particular, maybe it would be helpful to present the PEP to developers who use type annotations for runtime purposes, and to ask if they have concerns about the runtime semantics. The feedback could then be summarized in the PEP. I'm not sure if this is commonly done in PEPs, but it could be helpful here since a lot of developers still don't use type annotations regularly (or at all).
I also wonder if this new syntax would appease some of those Python users who've complained about what they perceive as the "bolted-on" nature of Python type hinting. In quite a few online discussions (outside typing-sig and other spaces with a lot of typing users) I've seen people who are unhappy about this aspect, in particular. I'm not sure how we could easily determine if this is the case, though. Jukka