So it's not a big deal, but the OP wanted to know if it exists in TrekLit and the conversation went from there to where? I mentioned my opinion that it went away because in the "real world" some people felt it looked silly, yet somehow my personal opinion is viewed as being illustrative of the fact that equality has not yet arrived because OBVIOUSLY my opinion is based on my male gender normative?
That is a circle in a circle in a circle - Skantception!
Both male and female humans wear non gender specific garb - PANTS!
The problem that arises is that most Trek fans acknowledge that the "ideal" future is one that is peaceful, inclusive, etc. yet some clamor for that future to reflect the most cutting edge and progressive thinking available at the current time.
For instance, a new Trek Series would undoubtedly be encouraged perhaps even required to have at least one LGBT character. Yet human culture embraces a multitude of ideas and mores, and a representative slice of a group of humans could contain any number of combinations, including religious individuals, monogamous heterosexual married individuals, and single, childless, asexual, genderless individuals. A recent Trek novel even had a crewmember who wore a hijab, a small detail that I thought was very cool as it showed a rare moment where religiously influenced cultural garb still existed in HUMAN culture.
I feel that it is a misplaced notion to expect that a specific character, costume, or event be placed within a story to PROVE that society in the future conforms to whatever the most progressive standard is at this current date. Why not just accept that whatever representative slice that the storyteller took of society in the 24th century did not include a person, place, or thing that is - by our standards - progressive?