You should believe in the Power of Shazam… DC does, enough to split that part of their universe into 2 films. One will focus on Billy Batson's journey to becoming Captain Marvel while the other will focus on his villain, Black Adam. Dwayne 'The Rock' Johnson has already been cast as Black Adam for quite awhile now, but the split puts him in the lead for one of the films. This comes from the meeting Johnson had with Geoff Johns, DC Films co-head. Johnson tweeted out an image of him at the DC office with the line: "hope, optimism & fun."
Johnson has been attached to the Shazam franchise since around 2008, but his popularity continues to grow and it made sense for DC to spin him out into his own film. The character of Black Adam has often been portrayed as an Anti-Hero, often in comics by Johns, protecting his people while devastating any and all that stood against him.
No other casting has been announced, so the search for a Captain Marvel continues… at least for DC's version.