Suicide Squad: the movie.
It’s going to be a near-impossibility to get a Justice League movie together. So, this is even a longer longshot. But it would be a hell of a ride.
This would only focus on the supervillain incarnation of Suicide Squad.
Take Amanda Waller from the Green Lantern movies and expand her role. She’s going to be Nick Fury, but for evil. (Although Waller always thinks she’s doing good.)
She recruits Sinestro, Cheetah, and Scarecrow from the Green Lantern, Wonder Woman (see my other post), and Batman movies. And maybe a Rogue from a Flash movie. She also grabs some new villains like Deadshot (because you can’t have Suicide Squad without him.)
They are up against a villain more powerful than all of them combined. And more evil, too. I’m thinking Omac. In this version, Omac is created by the government, but it has become uncontrollable. So they form the squad – a group of expendables – to clean up their mess. Throughout this they learn that they are being used. They go to rebel against the big, bad government. However, Sinestro is really playing them as pawns, too. Building up the fight between the government and the Squad so that they’ll be too distracted to use stop him until it’s too late.
The villains react very strangely. They never worked as a team before, so they have to learn that. At least one villain actually likes playing the hero. Deadshot doesn’t care who’s paying his bills as long as he’s got someone to fight.
Sinestro is too power-hungry; he’s biding his time and might be the main villain after the Squad defeats the enemy.
At the end, the Squad manages to destroy all documents relating to their incarceration or the existence of Suicide Squad. The last thing you see is one of the members, one who serves as a voice for the others, meeting with someone who will hire them as mercenaries. Perhaps this person could be Lex Luthor or someone that leaves a hint of a future story.