I think there are some, ah, highly unusual people who want to be raped by unattractive people because its even more degrading.

But anyway, the way that rules could be made to work for everyone would be to institute a code like 'everyone wearing a red hanky wants to be raped'. With smartphones this could be made more sophisticated, and you could set statuses such as only wanting to be raped by people who are rated at least 3/5 on looks.

But this is still a way of giving prior consent in general, rather than legalised rape.