The whole thing a dream?
All right, I go ahead type out the obligatory praise for this masterpiece first:
Damn, this is a great movie, surrealism at its finest, Bunuel was a genius, yadda yadda yadda.
Now the theory: was the entire prostitution situation just another vision?
I'm leaning toward yes. Namely because of one line toward the very end which brings it all together for me. It's easy to miss, but it had an impact on me so I'm sure someone else got it too. When Severine is with Pierre in the living room at the end she says after his accident she doesn't dream anymore. ACCIDENT! Not attempted murder, but accident. I went back and listened to the French to make sure it wasn't a subtitle error and she did indeed say accident. This leads me to believe that the core of the film is but a surrealist dreamscape for Severine's repressive desires which are satisfied after her husband is no longer able to act as a man (paralyzed, therefore, no sex).
Think of Marcel. She created someone who is the complete opposite of Pierre: one is a doctor, the other is missing parts of his body; one is a gentleman, the other a criminal; one is compassionate, the other violent and aggressive. And of course as any good fantasy would have it, Marcel is completely infatuated about her and even killed/died for her. In addition to that, all the men wanted her at the whorehouse (much to the others' dismay).
I'm in favor of the implications that she suffered sexual abuse as a child and therefore see her as someone who does not want to be physically intimate with her husband because of her repressed sexuality. Her friend told her about another woman who became a prostitute and this planted the seed in her imagination to grow throughout the film.
She agrees to sleep with her husband once (not make love, just sleep next to him) after a particularly strange episode, but besides that she is frigid and distant. Once he is incapable of being physically intimate, she embraces him as the man she's loved and no longer dreams (as she told him). Now she is satisfied at having the love of her life at her disposal whilst keeping her purity intact. She's actually not a victim if you look at it that way, but quite a self-serving little bitch.
I could be completely wrong, but I think it is an interesting theory. Feel free to tear it apart or to call me a genius.