The "Iron Man" franchise has been the most lucrative of the Marvel films other than the two "Avengers" movies, but word is that a fourth entry may not be in the books until 2020 or after. According to Master Herald, Marvel Studios already has its plate full with 14 movies releasing between 2016 and 2020.
The year kicks off with "Captain America: Civil War" and then "Doctor Strange," eventually leading to the two-part "Avengers: Infinity War" and the "Inhumans" movie. Also added into the mix is the solo "Spider-Man" movie from Sony, which is also being considered as part of the Disney-Marvel cinematic universe.
It is also expected that Sony's "Spider-Man" franchise will branch out with its own sequels that will intersect with the Marvel Cinematic Universe so not only does Marvel need to be wary of spacing their own release dates but they'll also need to be wary of Sony's release schedule for "Spider-Man."
This leads to 2020 and beyond as the only viable schedule for "Iron Man 4" and by that time Robert Downey Jr. would be 55 years old, which could make it more difficult for the actor to continue playing an action-heavy role such as that of Tony Stark aka Iron Man. If the movie were to happen, it is possible the role of Tony Stark could be re-cast.
Master Herald also points out that Downey Jr. is also the most expensive actor on Marvel's payroll and as his involvement continues, it is possible that Disney and Marvel may refuse to take him for another movie if his fee is too high, even with the knowledge that the "Iron Man" films have generated billions of dollars for the studios.
However, the report also points that there are three untitled films in the Marvel schedule and it is possible that "Iron Man 4" could fill in any of those three slots. Many fans, on the other hand, speculate that these slots may be given to "Doctor Strange 2" or even "Spider-Man 2."