Margot Robbie debuted as Harley Quinn in David Ayer's Suicide Squad, before taking the lead in Birds of Prey and the Fantabulous Emancipation of Harley Quinn, and returning for James Gunn's The Suicide Squad.
Though the Academy Award-nominee's performances as the deranged antihero were praised by fans and critics alike, none of the above movies featuring Quinn proved to be box office hits. This led to Warner Bros. scrapping at least one other Harley-focused project (that we know of), which in turn led to speculation that Robbie may have decided to step away from the role.
Yesterday was the 30th anniversary of Quinn's debut in Batman: The Animated Series, and Gunn took to Twitter to share a couple of previously unseen The Suicide Squad production stills. A fan asked the filmmaker if we'd see Harls in the DCEU again, and he responded with a straight-to-the-point "Yes."
This obviously doesn't give us much to go on, but Gunn does seem pretty sure that Quinn will make her return at some point. This could suggest that he's aware of an upcoming project featuring the character, or may even have something in the works with Robbie himself.
Could Harley show up in Peacemaker season 2, perhaps? That seems like a long-shot, but then we never expected to see members of the Justice League appear in the season 1 finale, so who knows what Gunn has in store for us.