2) Catwoman
Catwoman is by far the most portrayed DC female character, with the anti-heroine being a fixture of just about every variation of the Batman franchise on screen. The DCEU surely won’t break that trend, then, so it would be nice to see Catwoman turn up in a Harley Quinn movie. Selina Kyle is usually based around her flirtatious relationship with Batman, so it would certainly be fun to see her in a film where the Caped Crusader is presumably (at most) a minor presence.
While Catwoman isn’t an out and out psychopath like Harley, Selina is a woman on the wrong side of the law, and both are besotted with those two eternal arch-enemies the Joker and Batman. As such, it would be fascinating to see these different but similar characters come together. If handled well, they could share a really great female double-act.