Following the critical (if not so much commercial) success of The Suicide Squad, DC fans are desperate to know where Margot Robbie's Harley Quinn will go from here. That's currently unclear, but there are a couple of projects that have been stuck in development for years, though, and could fit the bill. James Gunn's thrown doubt on Gotham City Sirens anytime soon, though, so that leaves Harley Quin vs. the Joker as one possibility.