First, the SC is postponing considering accepting https://www.python.org/dev/peps/pep-0646/
any further until Python 3.11. There's unfortunately not enough time before b1 to get requested updates into the PEP, discuss the PEP again, approve it, and then review an implementation thoroughly.
Second, this PEP is proposing new syntax for Python but that detail is barely touched upon. For instance, there isn't a direct proposal of what grammar changes that should be made. There's also no discussion of what the exact runtime semantics should be. While a lot could be inferred by "it's allowing * within indexing contexts" (which is basically what the PEP is proposing from a syntactic perspective), that isn't a spec. 😉 As such, we are asking that the PEP be expanded upon to fully explain the proposed syntactic change, it's impact on the language and it's spec, etc.
Once this update happens, we will be happy to look at the PEP again for consideration of inclusion in Python 3.11.
-Brett (on behalf of the SC)