Jason Momoa's name has long been circling Batman v. Superman: Dawn of Justice, but never in an official capacity and while today's report from HitFix isn't an official confirmation, there seems to be enough confidence behind it to take it seriously.
The report insists Momoa will have a cameo appearance in Batman v. Superman as Aquaman, a character that will reportedly be featured more in future films such as the rumored May 2017 release of the Untitled Justice League Movie, though a stand-alone Aquaman film was not one of the films mentioned in a recent report announcing the slate of DC Comics films Warner Bros. is expected to announce shortly.
As for this Aquaman business, it sounds like the take on the character will be a more modern one, featuring the brooding king of Atlantis and he's apparently not all that happy about the World Engine from Man of Steel and what it did to the Indian Ocean. In fact, it seems that's what the film will be about, a story of consequences for Superman as a result of the destruction in the film's final act with Batman coming in to say, "Shame on you Superman." Then again, it seemed to me, with the final scene in the film, that the world had moved on from that incident. Oh well, the film doesn't hit theaters until May 6, 2016 so it's hardly worth thinking about at the moment.
Momoa joins Henry Cavill as Superman, Ben Affleck as Batman, Gal Gadot as Diana Prince/Wonder Woman, with Amy Adams, Laurence Fishburne and Diane Lane returning from Man of Steel, Jesse Eisenberg as Lex Luthor, Jeremy Irons as Alfred and Holly Hunter in a role newly created for the film.