I was thinking last night about shows set in prisons, like "Oz" and "Prison Break" and "Orange Is the New Black", and it popped into my head so quickly that I spent the next fifteen or so minutes checking to confirm that it had never been done simply because it seemed so obvious: 'Arkham Asylum'.
I mean, of course they've done things set in Arkham. Grant Morrison did the classic Arkham story, but there've been tons of mini-series and one-shots about the history of the iconic mental institution where all of Batman's villains are kept, and the video game is a classic as well. But they've never done an ongoing series, and they've never done a series that focused on Batman's enemies. It seems to me like this is just a natural, perfect extension of DC's current focus on damaged protagonists and anti-heroes and grimdark, but it's one that has the potential to actually be done well. A regular series, set in Arkham, with the Batman villains as the protagonists as they try to survive life in the worst prison in the world.
You have so many interesting characters to play with. The Penguin, who somehow contrives to get locked up in Arkham despite having no apparent mental health issues, and who no doubt maneuvers and manipulates the other inmates to get what he wants. The Joker, a terrifying force for chaos who even the staff fears. The Mad Hatter, a seemingly gentle soul in his own way but one with terrifying depths. The Riddler, an unpredictable and manic prisoner who sees everything but gives out his secrets sparingly. The Scarecrow, who takes the role of psychologist with his own cellmates. Harley Quinn, a former staffer who wound up going too deep into her understanding of madness and has no way back out. There's a huge ensemble cast with built-in name recognition and fanbases, and you can rotate the cast as needed because they'd be constantly escaping to appear in the next Batman story. (You could even show the escapes.)
I'd have to brush up on my prison dramas if I wanted to write this, but it seems like such an easy win for DC that I honestly don't understand how they haven't done it already. It'd be the best elements of a crime drama mixed with a horror story, all featuring the most famous villains in the world. A no-brainer like this should at least get a trial, dangit! Who's with me?