I'm not believing it until I see an official press release from Warner Bros. If I do see that, I'll be incredibly disappointed that they think there's no way to make a good Justice League movie without tying it to the Nolan trilogy. It's like they noticed all of the money that Avengers made, but didn't notice a single thing about why it was successful.
Well.. they tried the Special Effects/Humor heavy version with Green Lantern and fell on their ass.
They see the broody and dark Batman movies that made a ton of money and were generally well received by fans and critics so can you fault them for adding up two and two?
Movie execs rarely understand the creativity of stories and the uniqueness of the brand they are supposed to control.. this is why they hire creative people but even that process is sometimes hit or miss depending on if the creative person is capable or his reputation overblown.
Whedon was a brilliant choice but even being very familiar with his TV work and Serenity i was hesitant if he could pull of a juggernaut like Avengers. Fortunately he did and Nolan has an equally impressive line of movies under his belt just with a different style so i'll give him the benefit of the doubt.