How about this: What is the probability of the Democratic ticket in 2016 having 2 women on it? I'd argue while unlikely not nearly as low as many would assume. The reason being that if Hillary is the nominee, everyone will as usual engage in the parlor game of guessing the running mate and there's no way the subject would be avoided. The press will openly look at the "list" and wonder if she could get away with picking a woman and some will clumsily insist it'd be impossible which is of course, an obnoxious assertion that would be met with serious pushback. Men have had male VPs for over 200 years. Why should Hillary hesitate to pick Klobuchar or Napolitano or some new female governor? Remember Bill Clinton jettisoned the tradition of geographic balance instead doubling down on another young Southerner. Maybe Hillary would try a similar move.
I agree in theory that a ticket with two qualified women could be just as acceptable as two male candidates, but due to electability reasons, it won't happen for at least a few more elections.
As for Clinton picking Gore instead of giving geographic balance, southerners are a Republican (-leaning at the time) constituency, so it would help make inroads, while women are a Democratic-leaning constituency, so there would be no comparable gain.
