Well first of all you’d have to think of the practical side of it, ie how we’d be led there to start with. How would people reproduce? Incubators for example? Would we have only one gender (eg only women, with infinite amounts of sperm frozen in sperm banks so that they could use it to have children whenever they felt like it, then genetically modified them to make sure they were girls)?
Or are you referring to a society where the gender exists, but is hidden (eg the dwarves in Discworld, where both men and women have beards and dress the same way, but actually have different genitals, which only matter when they want to reproduce)? This is actually feasible. I can imagine that, what with women shaving their heads and men shaving their chests, we can soon see a world of uniform, skinny people, all hairless.
Men will still have genitals, hidden under their clothes (the same clothes that women already wear), and women’s breasts would be so small as to be practically invisible (especially if fashion does away with bras and the tops are also unisex). There are already girls that could pass as boys, perhaps this type of neutral look could become the norm. And if everyone turns out to be bi, then gender will become insignificant. You could pick someone up at a bar, not knowing what they’ve got packed in their pants until you get home. Just like women today can be (un)pleasantly surprised with a larger or smaller penis, everyone in this society would then have to wait to find out whether their sex partner had a penis at all.
All this still sounds very far-fetched, and personally I’d hate such a scenario, but then again I’m a 20th century heterosexual male. I imagine that over the next couple of centuries our society could change towards that, and some people even today might find all this appealing.