There's a reason you haven't heard much about Shazam, the film that will star Dwayne "The Rock" Johnson as the anti-hero/antagonist Black Adam: there's simply not much to tell at this point. The film, in development for a current release of April 5, 2019, doesn't have a finished script yet.
In a Heroic Hollywood podcast, they said the script draft is still being waited on by Warner Bros. Until the script comes in, despite the general idea of the characters and The Rock's involvement, they're holding off on trying to find a director.
WB is typically running principal photography from around 15-11 months ahead of release for their current crop of superhero movies. By that schedule, the earliest they should need to go into active production is around January 2018, so there's no real rush on that end. Of course, Johnson recently said that he thinks the film will come out "earlier than that, I don't think 2019," so things may be accelerating.
Dwayne Johnson's very early signing for the film may indicate a cameo coming in an earlier film, or could have simply been WB trying to grab him before Disney/Marvel Studios tried to for one of their superhero franchises.