5. Idris Elba
Why He Could: He's an outstanding, supremely talented actor who has amassed a loyal fanbase with his work on shows such as The Wire and Luther, as well as his memorable cinematic performances in Prometheus and Pacific Rim. He endeared himself to a whole nation of geeks with his utterance of the phrase, "We are cancellin' the apocalypse!", and that might just be enough to win the comic book nerds over despite one obvious issue...
Why He Won't: He's black. There's no way around it, but given that Bruce Wayne has been traditionally white in every major iteration, audiences would likely reject a black Batman simply because it's not what they're used to or how they imagine the character. When Elba was cast as Heimdall in Thor, there was a massive backlash, and similarly, whenever chatter emerges about the man possibly playing James Bond in the future, it is usually met with controversy. Warner simply wouldn't dare risk the bankability of their franchise on a pitfall that is so obvious to avoid.