"I am only speculating," he said in an interview with the Tampa Bay Times, “But I will guess that [Robert Downey Jr.] is done. He has been doing the same role for over 10 years now, and I think as with any actor sometimes, it is time to move on." And by done, he's thinking it'll be the permanent kind.
"That is one way of doing it, but I’d only be guessing," he said. "I know this—I wouldn't want to recast Tony Stark. Who would want to try to top Downey? But, if Tony doesn't come back, they can put somebody else in the armor and start a new generation of Iron Man.”
It would be quite poetic for Iron Man to finish off the decade-long run of the superhero franchise since the Marvel Cinematic Universe all started with 2008's Iron Man. In the films, Stark continuously proved himself to be ready to sacrifice himself for Earth. The O.G. Avenger has even been replaced by others in the comic book world. Most recently, a black girl from Chicago, Riri Williams, took over his mantle as Ironheart.
As noted by Comic Book Resources, Layton gave Marvel fans Iron Man's famous "Demon in a Bottle" alcoholism storyline back in 1979 and created the character, Ghost, who appears as the villain in Ant-Man and the Wasp. He's also working on a film based on Valiant's superhero Bloodshot.