Some people really, really hate meta and think it ruins the show. Some people only watched the mytharc parts of the episode because of an "embarassment squick" that made them incapable of even watching the alternate universe stuff. And there was one post by a person who said that "true fans" don't like the direction the show is taking.

Dean would still probably have to be in the mdidle for me. Because angels are brothers on the show, and I just can't really get past the incest thing. But I could totally do it in a threesome where it was mostly the two of them doing Dean.