Black Panther is the first movie with a black lead in the Marvel Cinematic Universe, but he was almost superseded by Don Cheadle's War Machine.
In an interview with Complex, Black Panther screenwriter Joe Robert Cole discussed how he was introduced to Marvel's writer program. "At that meeting, they also said they were thinking of doing a War Machine movie," Cole said. "I pitched a concept and won that job to write the script but they decided, based on what Iron Man 3 was going to be, they weren’t going to do War Machine anymore. But they asked if I’d be interested in joining their writer’s program instead."
Iron Man is the leading man in the MCU, and his supporting character James "Rhodey" Rhodes is also a layered, complicated character that arguably deserves his own solo outing -- it would allow Marvel Studios to explore the militaristic side of his character that's typically been sidelined. Perhaps there's a chance of the War Machine movie being greenlit if Black Panther is as successful as it's poised to be.
Cheadle will next appear in Avengers: Infinity War, which opens on May 4.