Well most system games are really rules light, so adding new rules on top of them is probably not gonna fly real well. And since most games are systemless there's really not much need. Also these sex rpgs are almost never worth it and I usually just am thinking I could come up with something better than this if I needed to. And finally, adding rules to sex has never made it more fun.
So uh, without actually having read it myself, I'm skeptical.