2. Harley Quinn
Harley Quinn has the honor of being one of the first members of Batman's rouge's gallery to appear in another medium before being later adapted to the comics. Created by Bruce Timm and Paul Dini, Harley made her debut in Batman: The Animated Series and was almost immediately met with fan and critical acclaim. A former Arkham psychiatrist, Dr. Harleen Quinzel fell victim to the Joker's charm and joined his crew as his on-again off-again girlfriend. Harley is known to be head-over-heels for the Clown Prince of Crime, but every so often, she'll blaze her own warpath simply to spite the man she loves.
Why we shouldn't expect them: Now, out of all of the villains on this list, this may be the most polarizing suggestion. Harley has had a very strong following since her first appearance in the 90s; I personally love her and am thoroughly satisfied that she has had a large role in both of the Arkham video games. However, Harley just doesn't seem to work nearly as well unless the Joker is involved in some capacity. After all, he's the reason she abandoned her promising career. If WB is brave enough to do another Batman film in the near future that features the Joker, I'm not sure they'll want to waste their time and attention trying to fit Harley in as well. She's a very high-strung, high-energy character that shouldn't be half-assed, and for that very reason, I hope she sits these films out.