While I wholeheartedly disagree with those who act like Marvel has done everything right while Warner Bros.' and DC Films have screwed up royally, there's no denying the DCEU is kind of a mess. With The Flash still in creative turmoil and The Batman basically starting from scratch, Warner Bros. wants another movie to open in 2018 besides Aquaman, which just got bumped two months.
So what are their options? Variety's Justin Kroll says Gotham City Sirens, The Flash, Green Lantern Corps, Suicide Squad 2, and Dark Universe are being considered now, although none are anywhere near ready to go.
Sirens at least has David Ayer in the saddle and a star in Margot Robbie, and he proved with Suicide Squad that he can have a movie ready in a matter of weeks. That said, the results weren't exactly glowing, so we may not see a repeat of that. The Flash has lost a couple of directors already, and they'd have to work around Ezra Miller's schedule on Fantastic Beasts 2. Dark Universe has a Guillermo Del Toro script ready to go and Doug Liman in the director's chair, so it may be the best option.
Suicide Squad 2 just hired Adam Cozad as screenwriter, but that's about all it has right now despite the Mel Gibson courtship. That said, things could be about to change. Jeff Sneider mentioned on that popular
Green Lantern Corps was a long distance off for a reason, but Sneider adds that David Goyer, who was already working on the script, may just go ahead and direct it, too. That would solve a lot of problems and possibly move it up to start shooting this year. Goyer hasn't directed a major superhero movie since the divisive Blade: Trinity, best known for proving Ryan Reynolds would be a perfect Deadpool if given the chance.
Whoever WB and DC Films run with will have to get on the ball quickly. It's almost inconceivable nowadays for a major studio to only have one superhero movie a year, crazy as that sounds. You won't find Marvel with less than two, and next year they have three ready to go.