"Cis" and "trans" are different types of a person's.... what?
What are cis and trans alternate types of? I don't think it's "gender identity" because wouldn't that just be man, woman or nonbinary regardless of whether they're cis or trans? Cis/trans just being a qualifier?
If the answer is "I am cis" or "I am trans", what is the question?
Edit: Someone came up with the term "gender congruity" and (after looking up the definition of "congruity") I think this describes what I'm talking about perfectly.
I agree with what you're stating and I hope that that's where we are headed - there just being man, woman, and non-binary gender identities. For now though, as I see it, cis/trans become relevant in three ways (off the top of my head):
Medical situations - self explanatory
In pursuance of romantic/sexual relations - society is still at the stage where the visual perception of a person lead to certain presumptions. Not everyone may be okay with dating/having sex with a person who has different genitalia than they presumed that their partner would have.
[This point is my personal opinion] The visibility of people openly owning their journey can be a source of information, give courage to others who are undergoing the same journey and are scared or confused. I knew about my orientation way before I realized that there's a term for it or that their are others like me.