Warning! SPOILERS for The Batman.
Despite The Batman's introduction of Barry Keoghan's Joker, it's too early to recast Harley Quinn for Reeves' Batman universe. The Batman goes to great lengths in order to establish its rich universe separate from the DCEU, with grittier, grounded takes on a number of its characters already evident. However, with its brief introduction of Barry Keoghan's Joker, it follows that sooner or later Reeves will seek to secure a Harley Quinn for his universe, particularly as the character is currently more popular than ever.
The reason behind Harley Quinn's surge in popularity lies squarely with Margot Robbie. First cast as the DCEU's Harley Quinn for Suicide Squad, Robbie has since reprised the role for spin-off Birds of Prey and The Suicide Squad. Her take on the character became instantly iconic and has elevated Harley Quinn from a minor supporting character to one of Batman's most recognizable villains.
With Robbie as the DCEU version of Harley Quinn, it makes it far too soon for The Batman to potentially recast the role. While Reeves' theoretical take on the character would be an alternate version as opposed to a replacement, Robbie's Harley Quinn has too much of a future for the role to pass to someone else. In addition, The Batman's Joker will need to undergo more development before his Harley Quinn is introduced, or the focus of Keoghan's character will be on the pair's relationship.
As the DCEU has already proved there are more excellent Harley Quinn stories to tell, Robbie has a clear future in the role. Having a new Harley Quinn in The Batman's sequels would facilitate unnecessary comparisons, particularly when Margot Robbie's Harley Quinn is so universally appreciated. Despite it being possible for there to be two live-action versions of Quinn at the same time, it would only serve to further confuse and divide DC's fans, who currently enjoy a number of ambiguously overlapping alternate timelines.
There's also the matter of how Harley Quinn would fit into The Batman's world. Introducing Quinn to Keoghan's Joker would draw too many similarities between his and Leto's Suicide Squad version, and the dynamic between the two is something that the DCEU has already explored. Barry Keoghan's Joker in The Batman is a different take on the character according to director Matt Reeves, and he ideally needs to be given a chance to develop before he has a sidekick or love interest introduced.
With Harley Quinn's massive pop-culture significance and the character's overwhelming popularity, the temptation to incorporate her into The Batman's world is clearly tempting. However, in order to allow Keoghan's Joker the opportunity to stand apart from the DCEU's unpopular iteration, it would be far wiser to steer clear of recasting Harley Quinn for now. Whether or not The Batman sequels will introduce a new Harley Quinn remains to be seen, but it's certainly not the right time to recast the role.
