I believe it was duh brothers Warner & Paramount. Those are obviously 2 different entities but for some reason shared credit with each other. It's escaping me for the moment exactly which films & I'm not googling at the moment. So if WB & Paramount can do this, why not WB & Disney? Sure, they both want the whole pie but a film like SUPERMAN vs. THE HULK could be box office gold. JLA & Avengers, that is, if there's ever even a JLA film period. I'm sure other combinations could work. But they would have to put aside egos & do it for the fans I suppose. And the big bucks.