Practically the entire parser system is built around the Champion being either male or female, so adding any other options would mean going through thousands of instances of pc.mf, pc.mascFem, pc.isMale and pc.isFemale, redoing them all to allow for a new option and writing all of that extra content. There is an exception for pc.mfn and pc.isAndro if your character falls within a certain Femininity range and the game returns 'androgynous' results but that's about it and those aren't used that often.
The odds of someone going through and making all those changes is... minimal.