While doing press for Hercules in Mexico, Dwayne Johnson comments he is giving the role (whatever it may be) his heart and soul.
Johnson seems to confirm the role will be more of an anti-hero role, and that it is Black Adam.
Via La Nacion (translated via Bing):
"I try a character from DC Comics. It is the story of Shazam, but I can not say now whether (my role) is Shazam or BlackAdam. We have been developing for some time and I've been a fan of the antiheros. This in particular, I believe that we will do him justice. I'm putting my soul and heart in this role.
"I have always been interested in two characters in my entire career, they have been my favorites since childhood: GreenLantern and Black Adam... I think that we just advance announcement!
"It is now happening with Superman and Batman. Aquaman and wonder woman are. I'm excited and I know that the fansare excited too. DC and Warner Bros. they have a great mythology that we are going to respect, let's create something verycool and good foundation."