If there's a picture of the person on the ID, gender doesn't seem very helpful in verifying identity.
> The costs of the removing the requirement to display the holder’s gender on travel documents outweigh the benefits at this stage. The costs of the change would be more significant given the adverse affects on the operations of border authorities and the potential inconvenience for passengers.
In particular, they noted that border authorities use this data for risk assessment, the significant cost of modifying existing software that processes this, and that many countries would not accept passports without a sex marker.
[1] https://www.icao.int/Meetings/TAG-MRTD/Documents/Tag-Mrtd-21...
It's likely the picture will not be useful for determining their sex. This is why male / female was useful.
There seems to be this attitude taking hold whereby people who are (probably) overwhelmingly young and ignorant challenge everything they consider "not progressive". Clearly all the people who came before us were a bunch of idiots, so how could they possibly do anything right? It's an arrogant hubris. I say that as someone who is only in their mid 30s.
What I have come to realize is that everything people do (including those things I consider stupid, like organized religion) has a purpose. Once in a while the justification is weak. But if you find yourself wanting to eliminate some social practice because you think it's stupid and can't possibly comprehend why we would do a thing, that's a sign of ignorance.
Only after you understand the purpose can you start to talk about whether something is actually still useful.
This assumes an overwhelming adoption of the X gender marker. I don't think that's a reasonable assumption; I'd expect the number of folks who do adopt an X gender maker to be an incredibly tiny and easy-to-spot minority.