The new Batgirl DLC for Batman: Arkham Knight could be hinting at Justice League game. Players have noticed a hidden cameo by a notorious enemy of the League.
This YouTube video by Dribbz shows how to reach the Easter Egg. After crawling through a hard-to-spot vent in the Seagate Amusement Park, Batgirl emerges in a room with two glass capsules. One of the capsules is empty. The other is inhabited by Starro, a giant starfish-like alien.
Starro is a Justice League foe that dates back to the 1960s. He can fly and completely regenerate even if dismembered. However, his true power is mind control. He can spawn an infinite amount of smaller clones that can attach to human's faces and control them until they're moved.
His ability to turn people into his mindless thralls makes him a very dangerous foe. In the comics, he's enslaved millions of civilians and even a few superheroes. This is the kind of villain that you need a Justice League to take down.
This Easter Egg isn't the first time that Arkham Knight has made references to the wider DC Comics universe. The base game is littered with Easter Eggs about the world outside of Gotham. For example, players can see billboards for Metropolis and LexCorp, the company owned by Superman nemesis Lex Luthor.
There's even a message from Luthor waiting for players on Bruce Wayne's office phone. In the message, Luthor prods Wayne to sell off the Applied Sciences division of WayneTech where many of Batman's high-tech gadgets are secretly developed:
Come now, meet with me. I'm sure we can come to an agreement. A man of your refined tastes doesn't need an Applied Sciences division. He needs another billion dollars
A report from 2012 suggested that Rocksteady was planning a game based on the Silver Age of comics, which ran from the 1950s to the 1970s. One of the biggest developments from that period was the Justice League. Batman teamed up with several other superheroes like Superman, Wonder Woman and Green Lantern to combat global threats together.
Creating a Justice League game seems like the logical next step for Rocksteady Studios now that they've wrapped up their Arkham series. Each of their games has been bigger in scope than the previous one. Arkham Asylum was set in a mental institution, Arkham City put players in a walled-off section of Gotham, and Arkham Knight opened up the entire city for exploration. Expanding the story beyond Gotham and Batman himself would be a big leap but perhaps Rocksteady's up for the challenge. I'd imagine Warner Bros. would be all for it, too, considering their plans for a Justice League movie.