If we lived in a world where gender identity ideology ruled everything and was legally forced on everyone I would certainly identify as nonbinary, given that all the other alternatives would mean "I accept retrogressive and sexist beliefs about how women and men are supposed to behave and promise to follow them in my own life."
Also, even though becoming a trans man in that dystopian future would be the only way an AFAB (ha!) could seek equal treatment, to get there would require lifelong medical treatment and surgeries, and that is too high a cost, so nonbinary it would have to be.
But I very much doubt declaring nonbinariness in that world would reduce sexism and misogyny which would still be aimed at those who are AFAB, however they identify.
As we still have some choice, I choose not to belong to this new secular religion, but regard being a woman as meaning that I am an adult human being who inhabits a female body and who is treated as female by others.
That treatment includes being discriminated against, being sexually attacked and harassed, being judged lesser in all sorts of ways, and it is important that we can name those things clearly.
At the present time, a woman who chooses the nonbinary label reveals several things she perhaps is not intending to reveal:
First, that she defines 'woman' as a set of sexist stereotypes about femininity and a bundle of regressive gender roles for women.
Second, that she believes she can identify out of those, while women who don't make that effort obviously like being treated as Stepford Wives or Barbie dolls or pornified views of womanhood/femaleness.
Third, and assuming she participates in the new demands for inclusive language and the erasure of the female sex, that she is not only abandoning other women to being treated with sexism but further strengthens this by weakening any connection between being female and being a woman.
This comes about when 'inclusive language' is demanded (though not about the male sex) so that nonbinary female people don't feel excluded:
When the group of people previously called 'women' are now renamed as ovary-havers, wombcarriers, menstruators, or simply people-who-do-a-thing-only-female-people-can-do, the rest of us who don't believe in abstract gender identities are getting our definitions of our own womanhood invalidated and replaced by dehumanising synecdoches.