There is a strong case to be made that you are underestimating the role which biology and fundamental human psychology plays. You are also basing your assumptions on a far off future that isn't likely to come true for some time, if ever, given how little we still understand about how the brain works or consciousness.
I feel you are advocating more for a world in which we blend the 'fantasy' online realm with the 'reality' of the physical word. Anybody can be anything they want. There is some merit to this and it is an interesting line of thinking, but it still does nothing to disconnect the role biology plays in determining/influencing gender and gender roles.
You say this:
But you have no idea what that will look like. What happens when you disconnect a human being from their biology? Nobody has a clue, but there is no reason to think it will be a good thing. It is far easier to see how doing such as this may give rise to nightmare scenarios.
It's not about disconnecting completely from biology, it's about being in control of it, which we are already doing right now, to an extent, with CRISPR technology, and that's just the start.
But that's besides the point. Unlike nearly every other known species, we are not a slave to all of our biological impulses, even without direct of control it. As an example from the Rhesus monkey study posted earlier in this thread, while there are striking similarities between monkeys and humans when it comes the hormonal influences of gender norms, there's also a marked difference in humans and the power of ideation, where conscious thought can override impulsive behavior, resulting in inconsistent results in human behavior compared to our primal cousins. It's one of the reasons why humans aren't considered to have instincts in the same way that other animals are.
My predictions are based on the cognitive building blocks that we already have today. Of course, I don't know exactly what that will look like in the distant future, but the same can be said about any prediction we make that far out.
This could very well turn out to be a nightmarish scenario, I'm definitely willing to accept that alternative, but one thing that has been a constant with homo sapiens throughout our entire history is that we continue to build on prior knowledge to create a more artificial reality for ourselves, and I see no reason why that should change in the future. And of course this would affect gender and gender norms, as biology's influence on them would be meaningless if we had no means of conceptualizing them, and if the means to conceptualize gender norms (or any social norms) changes/advances, then it stands to reason that those social constructs would change/advance as well.