Here's some theories building off of some previous suggestions:
As an immediate spin-off of Arrow with roughly similar creative vision and budget: Suicide Squad. A twisted variation of the A-Team with one very big difference: all members are guilty of the crimes they are accused of, and their varying sentences are being carried out as commandos against extraordinary criminals (other super-criminals who may be shanghaied into the Squad later) and foreign terrorist networks (Kobra cult, Society of Shadows). Main members go by their comicbook identities as code names, recurring characters are also identified by codenames in briefing and debriefing. Deadshot, Cheshire, Boomerang, Plastique, and others are paired with Rick Flagg Jr. and Sergeant Rock as the basic team. Deathstroke is a freelancer often employed by the team. Crosses over with Arrow occasionally. Since it involves more obscure characters, lawyer problems should be nil. Superpowers could be introduced later, especially so wrongfully convicted Nathaniel Adam can become Captain Atom. Lots of potential in Deadshot's as bad boy archetype for CW Tweens, Atom and Plastique could also have immense UST.
As an ideal companion series and expansive action hero show: Gotham Knights. Basically, a Batman show with a large lack of Batman and a heavier focus on his supporting family, especially with Nightwing as the main protagonist, while Tim Drake is Robin at first with Barbara Gordon as either Oracle or Batgirl, with Spoiler and Black Bat being growing characters introduced in the first season. Antagonist are mostly limited to more obscure (Firebug, Scarface, mobsters, etc.) or more stable villains (Penguin) who could have a justified continued presence. Bigger and more iconic villains saved for special occasions (Joker limited to one episode during sweeps week, Ra's as Halloween special) and fewer villains made season long antagonists (Harvey Dent is initially cured and tries to help heroes before a villain pushes Two-Face back to the fore, Jason Todd is Big Bad of second season as Red Hood). As seasons progress, Nightwing could potentially become Batman, Tim Red Robin, etc. Biggest problem is both quality of production and lawyer permission to use characters: Batman, who would be a veteran campaigner and distant father figure, would have to actually appear occasionally.