During the Saturn Awards, Marvel’s president Kevin Feige revealed a deleted post-credits scene from Iron Man that ultimately did not make the final cut. The never-before-seen clip hints at the MCU's connection with Spider-man and the X-Men.
In the deleted scene, below, Samuel L. Jackson‘s Nick Fury approaches Robert Downey Jr.’s Tony Stark to suggest the Avenger Initiative for the first time. “As if gamma accidents, radioactive bug bites, and assorted mutants weren’t enough,” says Fury, “I have to deal with a spoiled brat who doesn’t play well with others and wants to keep all his toys to himself.” In the first line Fury clearly references the Hulk, Spider-Man, and, surprisingly, the X-men. Iron Man kickstarted the Marvel Cinematic Universe and this dialogue suggests Marvel's ambitions to include the latter two franchises into the MCU.
Unfortunately for Marvel Studios, while Spider-Man did briefly make his way into the MCU, the character has since departed the universe due to a split with Sony. As for Feige's X-Men ambitions, those could still be realized following Disney's acquisition of Fox.