Unknown, but certainly not any time soon.
At an event earlier this week, Marvel announced their Phase Three lineup which doesn't include a fourth Iron Man film. This means the earliest we could have Iron Man 4 would be 2019 (when the last Phase Three film is due to be released).
After the announcement, Kevin Feige was asked about the prospect of another Iron Man film. MovieWeb has some quotes from the interview, and he gave a somewhat cryptic answer:
If there are more years after 2019, then there will be more possibilities. I hope there are more years.
So perhaps they want to make another Iron Man film, but there isn't room for it for now, and a lot could change in the next five years.
Note, however, that this doesn't mean he won't be in future MCU films. For example, the trailer for Avengers: Age of Ultron
shows a new, traditional-style, suit, and an entirely new Hulkbuster suit. These must have been built since the end of Iron Man 3, so presumably blowing the old ones up didn't dampen his desire to continue building.