Del Toro revealed he’s recently finished the film’s “Bible,” will soon be announcing the screenwriter who’ll work from that bible, and that the film will star John Constantine (the blonde version) who is tasked with recruiting the other members of the team.
Del Toro said,
"On Justice League Dark, or Dark Universe, what we’re doing is we finished the bible. Then we’re going to start the screenplay with a writer we hope we can announce very soon. What I’m doing is the lead character that guides us through that is Constantine. Blonde. He is basically trying to recruit these guys. On Etrigan, I’m using Jason Blood in the time of Merlin. We get to their origin through the story. We don’t make the origin story at the top. We find it out as they each have mysteries to solve. Swamp Thing is at peace with who he is, but Deadman still needs to figure out who shot him. It’s all woven in. When I was a kid, my two favorite characters in the whole DC Universe were Etrigan and Swamp Thing, so I’m in heaven."
The fact that the script hasn't been written and a definite title hasn't been declared just shows where Justice League Dark Universe sets in Del Toro's future timeline. The visually poetic director is infamous for sandbagging projects for years closely editing every detail over many years. If Pacific Rim is a monumental hit it could be an incentive for him to streamline some of his other announced (and not so announced) projects.