Jeff Sneider is reporting that he got an email from a source on May 12 confirming that RDJ would be back, and that he'd be a Tony Stark from another universe who became Dr. Doom. He also says that this Doom will have a cameo at the end of F4.
https://www.theinsneider.com/p/robe...ps-movie-steven-caple-jr-i-am-legend-director