Despite the enormous success of "Iron Man 3," the fate of Tony Stark's on-screen future is in flux. Robert Downey Jr. is currently filming "Avengers: Age of Ultron" and is committed to a third "The Avengers," beyond that though there's...nothing.
The first hint though that Marvel is considering something has come this week during a recent New York City screenings of "Captain America: The Winter Soldier". A survey of filmgoers asks which post-2014 Marvel movie are they most interested in seeing: "Avengers: Age of Ultron," "Ant-Man," "Iron Man 4," "Thor 3" or "Captain America 3".
This is the first time it has been suggested a fourth "Iron Man" film is in consideration, despite the fact Downey himself has said he plans to retire the character after "The Avengers 3". It's expected that Marvel won't reboot but rather have a new actor come in and continue on (either as Tony Stark, or another character who will take on the suit).
If it were to go ahead though, it will almost certainly be after "The Avengers 3" and thus a part of 'Phase Four'.
Source: Cinema Blend