I do not believe that there are any pressing influences keeping a woman out of the oval office as of right now. More than anything there is probably an incidence of lower female representation in the political arena, with respect to men. I could see a female democrat before a republican but as circumstances prevail, it shouldn't be far off.
My vote? - Arkansas Senior Senator Blanche Lincoln, in 2020.
Reasons? - 1. Shes one of the youngest 2. She's somewhat centrist (a conservative democrat)