Batwoman's Poison Mary storyline is definitely intriguing, as is Margot Robbie's portrayal of Harley Quinn, and I'm sure the animated DC Universe series's portrayal of Harley and Ivy's romance is too, but honestly, I want to see a live-action portrayal of Harley and Ivy's romance that leans into the radical elements of the storyline. I mean, Ivy has two doctorates and a genius-level intellect, and the more complex, nuanced version of Ivy that shows up in, say, the DC Bombshells comic book series has rightly become an ecofeminist and queer icon. She's passionate about protecting the planet and its people and the reason she takes extreme measures sometimes is because the system will keep destroying the planet unless she shocks people into recognizing that they're endangering everything that makes it so life can exist on the planet. Harley has a similarly high-level intellect and is an accomplished mental health professional who gets drawn into the Joker's sick, twisted mind games and ends up being driven insane by him. No one recognizes the way the system itself has failed her, and she ends up in an abusive relationship with the Joker with everyone thinking she's just as horrible as him or maybe even worse. These two women are failed by the way the world as it currently is treats those with mental illness and those with a passion for environmental and social justice. They're marginalized, treated like dangerous villains, and simply not allowed to live their lives the way they choose, but with all the trials and tribulations in their lives, they find happiness and fall in love with each other. I know corporate properties (which is to say, all properties that currently adapt comic books into TV, films, video games etc) are unlikely to invest in a story that even just touches upon exactly how radical Harley and Ivy's romance really is, but it's a far deeper and more interesting storyline than the one we've seen in the main comics continuity or on screen.
In a perfect world, the Arrowverse's version of Harley would be another woman of color who'd show up to romance Poison Mary, and Mary would be canonically queer, but I suppose that's just wishful thinking.