I would like to propose that user agents will be able to pass a user statement regarding to its gender via an http header. the content must be a string, but not specified (as the definition of gender is flexible and might change from a culture to a culture and by time).
I see 2 main use cases:
Some languages have grammar cases which are gender-related.
The suggestion will allow to user to make a statement regarding to its gender once. Instead picking his or her gender or their gender each time.
Where would user agents get the value from? Also gender and what pronoun people prefer to be called can be two separate things. But this seems like something that can be implemented pretty easily by just passing your own request header. Then you can define it to be whatever you want.
Besides the stated concerns (privacy, fingerprinting, actively going against web neutrality and potentially enabling discrimination) the use case also seems to contradict itself. If the value is non-standard, it seems the benefit of custom grammar is hard/impossible to achieve.
Closing, as this risks blowing up. It wouldn’t be appropriate to send such information for the reasons given above (i.e., privacy, gender-based discrimination, etc).