This will lead to a spiraling effect- Fewer actual differences will lead to a lessening of socialized differences, which will lead to less actual differences, etc

I anticipate (and rather hope for) more differences. The main reason I would hope to see 'gender' differences to cease to be a significant concept is because people will explore whole swathes of new currently unthought of kinds of difference, relationship and community so that simple gender as we know it is lost in the crowd.