Robert Downey Jr. considered for multiple Marvel roles before becoming Iron Man, directors reveal

Robert Downey Jr. was almost cast in "Fantastic Four"
Robert Downey Jr. was considered for a superhero project before becoming Iron Man in the Marvel Cinematic Universe.
Marvel was considering a new movie version of the Fantastic Four at the time
Downey had come in for a general on the Fantastic Four and had met with the director and MCU honcho for Doctor Doom or something on another project
It's not too late to bring Downey back to the MCU for the Fantastic Four movie they're making now.