Two days ago, Warner Bros. won the most-recent (and most precarious) case brought against them by the heirs of "Superman's" creators seeking 50% control of certain aspects of the character's mythology said to have been created "apart" from what he was when their (crummy) original deal was struck (it's complicated.) Meaning that WB can now proceed to greenlight and start pre-production on any further "Superman"-related movie projects they choose. And they've wasted no time in making it official that they plan to have the "Justice League" movie out for a 2015 release date. That's one year after "Avengers 2," for those keeping track.
It makes sense for them to have been waiting for this case to shake out to make it official - I maintain that the people running these projects for Warners have very little idea of why these characters can and should work in movies, but they're at least correct that Batman and Superman are both needed to make the thing work (Wonder Woman, too, but they're in no danger of losing her rights and they still haven't launched a successful modern franchise off of her.)
One imagines that this means we can expect some sort of worldbuilding to be going on or teased at in "Man of Steel," but beyond that their plan is apparently to debut their new shared-universe versions of the other characters in "Justice League" and then spin them off from their (based on audience response and merchandise numbers, most likely.) If true, that move surprises me because it's a really, really, really good idea: Unlike The Avengers, nobody needs to be introduced to Batman, Superman and Wonder Woman as characters or the basic "ideas" behind them; while most of the other likely prospects are self-explanatory - The Flash runs fast, Aquaman is a "boy mermaid," Hawkman has wings, Martian Manhunter is a more overtly-alien Superman, Green Lantern is toxic as a live-action brand and probably won't be in the movie, etc.
The biggest immediate change of this announcement, of course, is that - with apologies to Marvel - the three biggest questions in superhero movie speculation are now as follows (in order):
Who replaces Christian Bale as Batman?
He's said he's done, and even if they could net him he's proven much too volatile an actor for the long-term planning this is going to require (see: Norton, Edward.)
Who plays Wonder Woman?
She'll have to be in there, since the Batman/Superman/Wonder Woman "trinity" is integral to the iconography as far as the mainstream culture (read: people who'll wonder why this isn't called "SuperFriends") and because she's the only female DC hero whose not the distaff-counterpart of a male hero that most people have heard of, and the pressure will be on this production to do better than "Avengers" did in terms of team diversity.
Who else is on the team?
As mentioned, diversity will be (and ought to be) a concern for this production. So while I'd lay money that, say, classic-Leaguers like The Flash are virtual "locks" (and I'm not kidding about Green Lantern - I'll be surprised if they bother with him) expect to see a push for minority characters like Static, Black Lightning or Cyborg (who was part of the "New 52" JLA recently) to get in there as well.