In an interview for IGN Jeffery Bell confirmed [http://www.ign.com/articles/2013/05/15/executive-producer-jeffrey-bell-talk-agents-of-shield-and-reveals-luke-cage-is-not-the-mystery-character] that it was not Luke Cage, may have possibly slipped that the first letter in the guy's name is "M", and also said some things about colorblind casting.
Honestly, we were looking for this part, and we just said, look, all our parts are open to all diversity. So the fact that we have a black dude who is awesome and it's J, was just because he was the best actor. It wasn?t like, ?You know who?!?
While Marvel reps have flat-out lied in the past, particularly when a mystery is guessed right out of the gate, my money is actually on Moon Knight. No, he's never been portrayed as a black man, but neither was Nick Fury before the Ultimates and neither was Heimdall before "Thor". Also, it would make the hoodie a clever costume choice. Still, it would mean they changed a lot of his backstory and gave him powers right from the beginning, so it might be a bit of a stretch, but I like banking on the long-shot.