I don't think that can really scale. How could you verify whether I am male or female without a reasonable amount of scrutiny, and then you are trusting them to keep your ID safe. In terms of the niche, that is my exact point. Maybe you are right, however I think the point of the niche is a small interconnected network of people who share one or a few traits deeply. SO is a bunch of people who are excited by one discipline and share knowledge surrounding it. Basically, being a woman probably has some idealogical overlap broadly, but it is a huge population to lump together. There will be conservatives, liberals, muslims, jews, christians, atheists, lawyers, people who have children, people who hate children, feminists, equalizes, stay-at-home moms, etc. The point is, people can connect on a lot of these levels but the narrower the focus the more tight the bond, IMO.