Alas, that was a long time ago, and while the X-Men and Fantastic Four could still cross paths, because these properties are expected to be rebooted within the Marvel Cinematic Universe, it’s not as though they can only cross over with each other. They’re now part of a much larger world filled with characters like Spider-Man, Black Panther, Captain Marvel and the Guardians of the Galaxy, and that opens the door for crossovers akin to what the mutants and Marvel’s First Family have been involved in countless times in the comics.