I doubt this is gonna flop. Tarantino has shot up in success since Basterds and Django. In class today tons of people who normally don't give a crap about film were talking about it. It also helps Leonardo DiCaprio hasn't been in a movie since he won his Oscar.
Tarantino is one of about five directors working in Hollywood who still guarantees box office power. Adding Leo into the mix as well as Brad Pitt and Margot and you've got a done deal, provided the movie is good.
Movie looks like a barrel of fun. I was sold just by this shot alone: