But here's where that gets hairy — if you run across a total stranger, let's say a biological male who completely "passes" as female and presents as such... aren't you almost 100% guaranteed to automatically refer to that person as "she", "her", "ma'am", etc.?

If that person instead identifies themselves as a male and uses male pronouns in accordance with what you're suggesting, it causes much more gender/sex confusion than what we have now, because if a certain subset of biological men can look 100% like women (and vice versa) and we would treat them as such without knowing their biological status, what's the point of them identifying as a man?

Your situation only works if gender pronouns and honorifics are abolished in favor of neutral ones universally (i.e. they instead of "he" or "she", Mx. instead of "Mr." or "Mrs.", etc.)