This should not be a market.
1. If you think the next president will be a woman you can buy shares in the woman candidate you prefer such as Hillary. This is essentially just asking weather you think Hillary will be the the next president.
2. This makes the presidential election market less interesting by dividing market activity because now there are two markets that ask the same thing meaning people will be split and it screw over the people that already have invested in the Hillary market.
3. It is too long term, like many of the markets on here. One week markets are perfect for users and it is in "predictit's" best interest because more people will use the site more often making more trades more often, generating more revenue. This also leads to free word of mouth advertising for "predict it", because people who use a site more often and are further engaged by weekly markets are more inclined to tell their friends about it by word of mouth or social media.
I'm fine with this as a market. There are other women with non-zero chances of winning (more importantly, perceived non-zero chances of winning). I think this is just as relevant as a market on which party will take the white house.
Sure some people will prefer to bet on Hillary or just be turned off by an ~18 month time horizon but clearly not everyone falls into that boat.