It's amazing how the word "pronoun" gets some people real mad.
I don't think SE will introduce what OP wants because it would be a lot of work for a small audience and it wouldn't be equally effective across all client languages.
But if this change came only those who used the option to change the pronoun could see the effect. You can't see or hear npc dialogue directed at another player. The pronoun change in npc dialogue would be a purely personal experience because reading/hearing npc dialogue directed at your character is already a purely personal experience. Of course players themselves can tell other players to use specific pronouns but they can already anyway so it's not as if what OP wants would make that happen.
I do think there are better things SE can spend their resources on, but in general I'm not opposed to allowing people to choose their pronouns in real life or a game. I just don't view it as an issue. I know many do, but for me it's a /shrug