Okay, I think we first have to agree upon some basic terms:
- sex
- legal sex: usually determined by the doctor at birth based on appearance of primary sexual features (penis/vagina). In most countries there are currently only two options
- biological sex: based on genetics, epigenetics, hormones, etc. as well as external factors like environmental toxins (I once saw a documentation about frogs that changed their sex because of some industrial waste and then got extinct in that region because there were only males or females) or operations (chosen by the individual or forced on them by well-meaning but uninformed doctors like genital mutilation of intersex individuals). Today’s science recognizes an infinite number of variations between a man (penis, testes, adams apple, androgens>estrogens, voice break, male body type & hair distribution, etc., etc. …) and a woman (vagina, uterus, mammae, female body type & hair distribution, etc., etc., …).
- gender: an infinite spectrum on which you identify yourself independent of your biology, legal status, societal pressure or whatever. It’s not a choice, it’s just your identity.
- sexuality: whether you are sexually attracted to gender-binary people of the “opposite” sex (=heterosexual), the “same” sex (=homosexual), both (=bi-sexual) or not (only) to gender-binary people (pansexual, gynesexual, androsexual, scoliosexual, etc., etc., …). Independently of what gender(s) you are attracted to whether you are monogamous or polysexual as well as the asexual-subspectrum and other aspects also fall under sexuality.
- romantic orientation: like sexuality, but not about who you are sexually attracted to but about romantic interest. You can be sexually attracted to one gender, but romantically to another. You can be asexual, but still be in a romantic relationship or be aromantic, but still be in a sexual relationship.
So if we go into this hypothetical:
If we hypothetically used “gender” as a term based on DNA then the presence of a 3rd gender would not be counter-factual, as there are variations in the DNA too. You can be XY (=male), XX (=female), XXY (=Klinefelter ‘Syndrome’), XYY (XYY ‘Syndrome’) or be born with any other genetic variation (Syndrome, deformity and condition are words that should not be used. Being different doesn’t make you sick. It only makes you different.).
Yes, but why pick and choose two that you specify and degrade the others as unspecified? Either don’t specify any or specify all.