What does this term really mean? If it's only 'not-quite-male' or 'not-quite-female' then that's nothing new. There were always men and women about who were not 'typical of their sex'. They were however made to feel conscious of their difference, and there was no official recognition of them. They were 'odd' and not 'normal'. So I think one big difference about the modern concept of gender-fluidity is that it is presented as a proper thing that someone can have, and not a sign of weirdness. A state as good and as wanted as any other. A natural state too - an innate thing, not a mere lifestyle choice; fundamental to a person's nature; unalterable; incurable.
In a gender-fluid world formal gender doesn't matter. We are all just people. Being 'male' or 'female' or 'something in between' doesn't affect relationships and the work one does in any way. People can pair off - or not - as they please. Mutual attraction and commitment is based on any of a wide spectrum of possibilities - there are no rules - and the only basis for assessing 'success' is whether the persons concerned are happy together. If babies are wanted, then couples physically capable of creating them will seek each other out. Some questions will have to asked of each other, but that's their private business. All dealings with the agencies of government, all dealings with anyone at all, are on the basis that people are individuals and their gender cannot affect their treatment, excepting only practical matters such as their age, physical size and shape, and state of health. The essence of gender-fluidity a doing-away with precise labels - avoiding making precise definitions that discriminate between people.
It sounds Utopian.
I can't see it being fully realised. Even if we suppose that a third of all human beings would like to be regarded as specifically 'gender-fluid' - neither male or female, but free to be something else - that would still leave two-thirds of humankind dissatisfied with that description and wanting to be regarded as 'definitely a man' or 'definitely a woman'. Because that would be the comfortable, most appropriate way for them to think of themselves. I'd be in the 'definitely a woman' camp, because if given the freedom to select a less plain and ordinary set of companions, that's where I'd still always go. And I believe that that a lot of people would do the same, and naturally gravitate to one of the two main camps. Birds of a feather do flock together. Human beings like to be with others of their own kind. I do know which birds I want to fly with. And what their brand-name is.
And there are other things as powerful as gender, if not more powerful. A person's ethnic background, intelligence, and income bracket, to name just three others. These things push and shove, clamp down and smother. A widespread acceptance of gender-fluidity won't necessarily lead to a general rearrangement of society. Other influences will shape it too. It would be nice if gender-fluidity - as a new factor - helped to create a better world in which everyone were valued, whatever variety of person they might be. It may have some effect. But I can't see it as the determining factor. Nor can I see progress in attitudes towards gender bringing about a homogenised world.
I'm not at all dismissing gender-fluidity as a passing fad, or something that doesn't matter. Of course it does. Anything that makes life fairer and more meaningful for the zillions of persons 'stuck in the middle' must be worth adoption. I've become aware, though, of a certain zeal connected with the notion of gender-fluidity - as if a gender-fluid person is ipso facto a more deserving human being than any other sort, justifying (certainly in some cases) bad behaviour and rudeness. Not in my book.