This is first and foremost a rumor. The rumor is from Batman on Film and well…their “Industry Insider” claims that the Justice League movie’s universe will be different from the universe of Man of Steel and the next Batman reboot movie. This brings more of a “huh” moment because it doesn’t make sense and at the same time it would be more beneficial for the movie.
The con of this rumor is why in the world do you want a different universe for this movie? The whole point of the Justice League is for DC’s superheroes to come together and save the world. It just disrupts continuity and confuses the crap out of people especially if it’s not done right. Which is the biggest fear right now.
The pro of this rumor is that a different universe helps the writer(s) create a better movie for viewers. It allows the writers to be able to have unlimited powers of creativity. I’m all for creativity if it helps with the story and the aesthetics of the movie. Kudos to Warner Bros. if they think they can really pull it off.
Source- Batman On Film