To be fair, this isn't a continuity thing. Despite its name, it's part of Black Label (however much longer that's going to exist thanks to the puritanical cowards in charge of DC right now) which isn't part of regular continuity. It's not really about detailing the history of the DCU but more about what that history would look like from the perspective of minority characters - at least, that's my take away from it.
Whether that's of interest is another story. John Ridley is a very fine writer but however much the premise has potential, I'm more than a little tired about everything being about the colour of your skin. This is not to condone racism or to deny that it's not still a huge problem throughout the world but I'm highly dubious of the idea that the way of combating this is by making skin-colour a person's defining characteristic. It negates the individual and it negates the cultural differences between people of the same skin colour. And, most simply, I just don't find this kind of reductiveness remotely interesting.
Sorry to get political but this is a book that's calling for it. Also, please note, I haven't written it off completely. If I hear good things, I will almost certainly buy it in trade. It's just that its main hook has me rather weary of it.