Smith and Margot Robbie were the only holdovers likely to return from director David Ayers' initial antihero team-up, with James Gunn taking over as writer and director following his ouster from Marvel's Guardians of the Galaxy Vol. 3.
With Smith leaving, however, Elba was reportedly the "first and only" choice for both Gunn and Warner Bros. Pictures to take over the role. Robbie is still slated for now to come back as Harley Quinn, while the rest of the cast remains unknown.
Elba is not just a star in his own right, but a genre regular, appearing in films such as Pacific Rim, The Dark Tower, Prometheus, Star Trek Beyond, Marvel's Thor trilogy, and the upcoming Fast & Furious Presents: Hobbs & Shaw. He's also been mentioned often as a possible successor to Daniel Craig in the role of James Bond.
After some time in development, with Ayer departing the project and director Gavin O'Connor spending a brief amount of time working on it, The Suicide Squad picked up speed once Gunn came on board. The studio is said to be pleased with Gunn's script, and Elba's involvement would likely get the train out of the station even faster.
The Suicide Squad is scheduled to come out on Aug. 6, 2021.