This comes as welcomed, truly exciting news. Tracing back to 2014 Downey Jr. disclosed to Variety:
"There isn’t one in the pipe. No, there’s no plan for a fourth Iron Man.” And that has been Downey’s stance in most of his public interviews. It seemed as if the Iron Man solo films with RDJ in the lead as Tony Stark were over. But it seems like that may have changed sometime recently."
Well well, now we've an encouraging update via a segment Robert Downey Jr. was filmed on during Nightline. It's short and sweet, clear, and to the point:
"I feel like I could do one more."
Alright, let's build on that RDJ. This is the first time Downey Jr. has spoken on record about being willing to do Iron Man 4.