Iron Man director Jon Favreau has confessed the famous Nick Fury post-credits cameo was ‘a lark‘ aimed at fans.
But I thought the idea of Nick Fury being Sam Jackson would be really fun, because when Nick Fury was reimagined in The Ultimates (comic book) they recast him as Sam Jackson, and I thought that that would be a really good nod to the audience.
Iron Man laid some key easter eggs for the Marvel Cinematic Universe, such as Agent Coulson working for S.H.I.E.L.
It was too risky and expensive, and all it would take is for one of the movies to bomb to derail the entire plan.