It's been three years since Robert Downey Jr. last suited up for Iron Man 3, and ever since he's been making appearances in other characters' films or as part of the Avengers. Talk of the fourth film has mostly consisted of Downey teasing the possibility, then quickly taking it all back, sometimes in the same day. Others, such as Gwyneth Paltrow, have said a sequel definitely isn't happening, but that door has to remain open, even if it's just a tiny bit.
Downey opened it again just a crack in a recent ABC story focused on Captain America: Civil War, which we know will heavily feature Iron Man. When asked about an Iron Man 4, Downey responded with "I feel like I can do one more".
And why not? He's feeling good enough to commit to Spider-Man: Homecoming, and of course he'll appear in the two part Avengers: Infinity War and who knows what else beyond that. His past statements have to be taken into consideration, too, and right now it looks unlikely a sequel will ever happen. We keep expecting Iron Man to take a backseat and pass the torch. It sure doesn't look like it right now.