I think if the DCU is to go the way of MARVEL, and open up a whole shared universe, they should take another stab at a CATWOMAN solo movie...
They need a GREAT script, that fits So neatly into the Universe they're creating at DC. They Should introduce Harleen Quinzel, (pre-HarleyQuinn). Though not dwell on the character, just enough to establish her. She should be a psychiatrist at Arkham. Hasnt yet met the Joker, and she is analysing her patient, Pamela Isley.
As much as I'm dwelling on Harley quinn, Its only because I cant think of a story strong enough for her, that's why I ask the question (how could they pull it off).
At the end of the catwoman film, I think we should have it set up so that HARLEY has somehow met the joker, Briefly. Though just enough to get into her head, and show just what he is capable of with such ease.
From there on i imagine she would show some element of infatuation. Thus carrying onto her next meeting with Pamela... End of The Catwoman Film.
Setting up perfectly for... - GOTHAM CITY SIRENS .!.The Movie.!. LoL!