Those of you hoping against hope that Joss Whedon would somehow be the savior of the Justice League film are bound to be disappointed by this news. Warner Brothers and DC have been saying all along that Whedon was brought in solely to help realize Zack Snyder's vision of the film, and not necessarily fix what they perceived to be a flawed film. It seems the evidence actually bears this narrative out because according to producer Charles Roven, the film is still at least 80% Snyder's film.
In an interview with The Washington Times, Roven—whose been a producer on Batman films dating back to Batman Begins—admitted that Whedon's contributions in no way overwhelmed what Snyder had already done...
“The goal is to make sure when you’re watching the movie, it all feels cohesive,” says Roven. “That imprint that Joss had, some aspect of it is going to come out in the direction, but the actors are already pretty much down the road on their arcs. Let’s just say 80, 85 percent of the movie is what was originally shot. There’s only so much you can do with other 15, 20 percent of the movie.”
So there you have it direct from the source. While Whedon's contributions are sure to be noticeable to the fans, I'm betting that the casual fan won't notice any real difference between this and Batman v Superman, beyond the aspect ratio. And even then most people have no idea what I'm on about.