The thing is, I don't find Wolram's observation to be generally true. I don't find gender separation to be weakening at all. The only big change I see regarding gender is that there is increased tolerance of gays being openly gay. So, a lesbian can walk into a market dressed like a truck driver, if she wants, and be treated like any other customer, but that's a recognition of something that's always been there and suppressed, rather than a general weakening of gender roles. Social enforcement of gay rights is a political, human rights thing, just like any minority rights, and didn't come about due to some erosion of gender identity. It happened by sheer force of political correctness.It's quite simple. There is no longer any great social pressure on girls and women to be girly and womanly because traditional gender roles are weakening and fading.
If women dress down more often, and I'm not sure they do, I don't think it has anything to do with gender roles. It would be better explained by the reasons Sophia gave, and by what you said here:
The motive is not to be more masculine and less feminine, it's to be more relaxed. Women dressing down when they can get away with it has been going on for ages. I have noticed an increased tolerance for casual, but that's a fashion thing that could change tomorrow if something happened to push it the other way.And it's just a fact that jeans, t-shirts, and close haircuts are just much easier and more convenient.
Traditional gender roles have been weakening and fading, but the product isn't that women dress more masculine and men more feminine. It plays out as women being allowed to take on jobs and professions from which they used to be excluded due to gender. Thinking back to all the woman doctors I've seen in the past 20 years, I recall most of them wearing skirts. With one exception, they all had longish hair. I don't see women wanting masculine jobs; there's been no rush by women into auto repair, machine shops, welding, or garbage hauling. What they really want is the good jobs.