The story doesn't include an actual quote from the actor saying he has been cast in this Marvel Phase Two sequel, but it does say that the actor, "has a part to film in the next Avengers movie," along with his Miles Davis biopic Kill the Trumpet Player.
What's interesting is Don Cheadle's Marvel involvement has been limited to just Iron Man 2 and Iron Man 3. He did not appear in last year's blockbuster Marvel's The Avengers. However, while promoting Iron Man 3, the actor did hint about having conversations with Joss Whedon about appearing in Avengers: Age of Ultron. The actor also mentioned visiting the set of next year's Captain America: The Winter Soldier, but it hasn't been confirmed if James Rhodes actually appears in the sequel or not.
It's also worth noting that, at the end of Iron Man 3, Tony Stark (Robert Downey Jr.) destroys all of his Iron Man suits, with many fans wondering how Stark would fit into the Avengers: Age of Ultron story without his high-tech suits. However, James Rhodes' War Machine and Iron Patriot suits were not destroyed. Is it possible that Rhodes could be subbing for the iron-less Tony Stark?
Joss Whedon is directing this Marvel Phase Two sequel from his own screenplay, with production scheduled to begin in March 2014.