Let me preface this by saying I am not someone who is working on the game, but do know someone that is. I'll share all the details they have with me.
>Possible titles
Justice League: Crisis, Justice League: New Crisis, Justice League: Infinite Crisis
Seems they haven't settled on a title yet, but they have a new staple in Crisis. Kind of like how Arkham was to their Batman series.
>Developer
Rocksteady
>Systems
Xbox Scarlett/PS5/PC. You'll hear more details on Xbox's new system later this year with a full reveal early 2019. PS5 will be announced in early 2019 as well.
>Type
Single Player/Co-op. You can switch between characters like in Arkham Knight. The campaign can be played both ways, but there's also a different game mode catered to multiplayer.
Also, it's GaaS, so expect a ton of DLC content. They're gonna have something similar to Hitman with episodic DLC.
>Characters
Superman, Batman, Wonder Woman, Flash(Pretty sure it's Wally), Green Lantern(Hal), Cyborg, Aquaman.
>Cities
Metropolis, Gotham, Keystone(why I said it's probably Wally), more others through DLC.
Each city is a bit bigger than AK, and just as detailed.
>Villains
Main big bad is Starro. As the episodic stuff rolls out you'll see Brainiac and even Darkseid.
>Story
All the heroes are pretty early on in their careers. Batman's still considered an urban legend to anyone outside of Gotham, Superman isn't the "world protector" yet, and WW is still on Themyscira. Aquaman's still in the sea, GL is in space, and Wally isn't even a hero yet.
>Gameplay
From what I hear, it plays just like the Arkham games, except more refined and "opened up". Guessing that's for the heroes that can fly and such.
>DLC
A lot of the DLC will have new cities and new playable characters. Green Arrow, Hawkgirl, Martian Manhunter and probably a lot more.
They're expecting this game to last for years, so I wouldn't be surprised if this game ended up being like Destiny in the sense that it gets updated constantly.