He should be cast as a James Bond villain who was passed over for a promotion in MI6
Considering the amount of campaigning that he did to being cast as the next (and first Black) James Bond, I think it would be a lot of fun if he got a role as a villain in a James Bond movie. Let's face it, he is getting up there in years, so the window of opportunity for him to being James Bond has been passed. He could pour his heart and soul into this villainous character and make the audience convinced that he has his reasons for his grievances and that he might have a point. That type of motivation always makes for the best villains in fiction.
Would the above be too meta? Would that be viewed as a step down for Idris Elba? He might not have achieved his dream of playing James Bond but if the script is right and the part is well-written, he can get the consolation prize of being a great and memorable Bond villain.