You're 100% pedantically correct, passing a NULL pointer as the corresponding argument to %p is fine... But that's really missing the point, since we're discuss

You're 100% pedantically correct, passing a NULL pointer as the corresponding argument to %p is fine... But that's really missing the point, since we're discussing %s and the only sensible general interpretation of this discussion presumably includes a "(when the other arguments mean the NULL is actually UB)" on everything. (E.g. the assertion for non-NULL-ity would go on the branch of printf that handles %s.)