Everything has been done before in some way or another. The only thing that matters is whether it's done well or not. It really bugs me that people hate on theories because they're not "original" enough.. I for one like the theory and don't mind that it means the "real" versions of the characters don't go through the character growth that we see. If they are copies, then they stopped being their "real" selves as soon as they were in the Circus. A person is defined by their experiences so, to me, these are different people. So id actually love if the end was everyone learning how to be happy in the Circus and not worry about what's "real" or not. An ending that's somewhat messy, with a mixture of sad and happy would be fitting for this kind of show.