I think the initial question of this thread has been answered, and I agree with much of what has been said! There’s one more perspective I can add on the topic of pronoun customization that I don’t think I’ve seen anyone mention yet.
Games have the power to facilitate playful, productive exploration of identity. I know that roleplaying games, broadly defined, have served as an especially invaluable and impactful tool for a lot of people (myself included) to try out different pronouns and safely explore their gender through roleplay. In this aspect, character creation isn’t only giving players the opportunity to roleplay their real-life identity but to actually try out a new gender identity/pronouns. This is more typical of video games and TTRPGs, I think; but I see no reason why this kind of exploration wouldn’t take place in IF.
If that is a group of potential players that an IF author would specifically like to support (people who are questioning/exploring their gender); and if the author is creating the specific type of game where the player experiences the story more less vicariously through the PC (although not necessarily as a self-insert); then a wide range of PC pronoun options can become much more meaningful than some sort of perfunctory inclusivity. It can be a real feature!
I wrote very extensive PC pronoun customization for one of my games, The Path of Totality. This included support for custom neopronouns, but it also included rolling pronouns (he/they, she/they, she/he, and they/she/he); a feature that I haven’t encountered in any other game/IF. (The method by which I scripted this is described in my postmortem under the Technical Highlights section.) Now, I certainly do not think this is in any way a “requirement” for every game with character customization! I just wanted to make that extra effort because it was highly relevant for that particular project.
But as others have pointed out in this thread, a gender-locked, preset PC can be completely appropriate, valid, and sometimes necessary, depending on the IF. As a nonbinary person, I will never feel excluded to “have” to play as a character with a fixed gender (I actually enjoy roleplaying as characters of all genders!). But I would feel excluded by a game that features in-depth character creation with personal pronouns but doesn’t include, at minimum, they/them (and preferably custom input for neopronouns as well). All of the above is completely relative to the type of game you are making, the audience you want to serve, and your goals as an author!