In what is currently being called Knights Of The Round Table: King Arthur, Elba is wanted to play not Arthur himself, but a version of Bedivere, who is credited in many of the interpretations of Arthurian legend as a noble and loyal member of the King's knights. In Ritchie's take – which features a script by Edge Of Tomorrow producer Joby Harold – he's apparently an older, wiser warrior and a right-hand man to Arthur's father who makes it his mission to train the young man for his true destiny. It would also represent a RocknRolla (2008) reunion for Ritchie and the actor.
Ritchie is still putting the pieces together on this one, and is currently on the lookout for an Arthur and the rest of the main characters. And nothing is known about how the film (or films, given that this appears to be another embryonic franchise) will deal with each part of the saga. The director may not have a locked in cast yet, but he does have a release date, with Warner Bros aiming for a 22 July 2016 release.