Well we're both speculating, but I believe AI will advance to the point it can reliably animate a 3D animated "girlfriend" in a virtual environment and then learn how exactly how to maximize pleasure and create erotic stories. With more advance teledildonics being able to simulate different types of sex it could become better at that then the best "courtesan". Fantasy is often better than sex already, but what happens when you have visual, physical and erotic narrative woven together?