Calling it "gender" instead of "sex" would really fuck up the narrative for these people. A persons sex is scientific standard language. A persons gender is how they feel at that particular moment.
I think this is a great way to start fighting back and changing the narrative.
I have been doing this exact thing, and its a strong argument.
There is no reason on any form to ask how a person feels... I feel that way about a majority of forms as it relates to sex too.
Austin Powers ruined Sex on a form, and people tend to put gender because they don't want to hear the joke "yes, please"
Maybe that was the intent?