Sooner or later, the wheels are going to come off the Marvel gravy train. No one can maintain the level of quality and success that the studio has had since 2008 with the first Iron Man, not in an environment where as many things can go wrong as can go wrong in big-budget film-making.
But seeing as even a film this "doomed" by any conventional wisdom can be as good as it is (which is, make no mistake, quite good), I'm not sure what can derail Marvel.
Because Ant-Man is yet another winner.