There's a market for absolutely everything.
Hot single girl sites make good money mostly because the girl appeals to the owner of the (tgp) site that promotes the site
I personally believe that REAL amateur, non-professional model sites would do great. People are getting fed-up with the silicon filled girls who look they came out of the same mold. But of course, that's just my opinion, as I know I am not one bit excited by the usual porn slut.