The first MCU movie already had big plans.
Many people like to state that when Iron Man launched in 2008, Kevin Feige was just throwing a dart into space and hoping for the best. Critics claim that at first, the MCU was just a shot in the dark which wasn't meant to get this big. Feige just proved those people wrong. As reported by Entertainment Weekly, at the 45th annual Saturn Awards, Kevin Feige was presented with the first-ever Stan Lee World Builder Award. Afterward, he revealed a deleted post-credits scene from the first Iron Man that shows Nick Fury referencing both Spider-Man and the X-Men.
“We pulled some things out of that vault that we said, ‘We’ll never show this to anybody, put it away,'” Feige stated. “We’re bringing them out, we’re putting them on this disc, and I’m about to show you a deleted scene that has never been seen by anyone before right now.” The scene shows Fury with his back to the camera as he begins his monologue. Fury speaks of “gamma accidents, radioactive bug bites and assorted mutants” before complaining about having to “deal with a spoiled brat who doesn’t play well with others and wants to keep all his toys to himself." He then brings up the Avengers Initiative. The scene was replaced by the one we all know, where Fury does almost the same thing, he just doesn't mention the X-Men and Spider-Man. This deleted scene proves that Feige was thinking about the X-Men and Spider-Man before the first Iron-Man even launched. Now that's world-building.