Is this an international first, by the way? If so, I wonder if other countries will adopt this "X" designation
The really radical thing to do would be to only issue passports with an X in the "sex" field. That way non-binary people wouldn't be treated any differently.
Now, should it be on there? Maybe? But if it must be, having an opt-out option is important, because people may not look male or female, rendering making identification less accurate. That's before we get into gender, where forcing someone to pick male or female when they may be neither is rather dehumanizing.
Do American passports have all those things?
I don't see any of those printed on mine in any obvious way. There are no fields for them like there is for sex. They could be in the electronic information, though, or encoded in the long string of digits at the bottom of the passport.
Some do. My driver's license is a also a passport card and has all of those except skin color.
Also even today US government discriminates against women when issuing visas in certain countries.