It was previously thought that Iron Man 4 might be in development as apparently the movie was mentioned on a Marvel Studios audience questionnaire.
However, now it is learned there are no current plans for Iron Man 4 according to Robert Downey Jr.
"There isn’t one in the pipe,” Downey told Variety. “No, there’s no plan for a fourth Iron Man."
The report also mentions Robert Downey Jr. was reluctant to sign on to anymore superhero films besides the two Avengers sequels.
When mention was made if Robert Downey Jr. would let someone replace him as Iron Man, the actor laughed it off.
“I like that the idea is that it would be up to me, like I’m casting director for Marvel,” he laughed.
From the recent statements above, we can gather either Marvel hasn't come up with an agreement, or Robert Downey Jr. didn't accept the offer.
July also saw Marvel Studios president and producer Kevin Feige mention there will absolutely be more Iron Man films and compared the character to a Batman or James Bond, with the reference obviously meaning new actors for the role of Iron Man at some point.
The Avengers 2 hits May 1, 2015 with "Age Of Ultron; The Avengers 3 is speculated for a 2018 release.