i have heard mention that they have also revealed The Flash will be being cast
with that and the inclusion of Wonder Woman my take on this is that Man of Steel takes place in a universe in which The Justice League already exists and he's a late (and somewhat ignorant) arrival to the party so to speak.
if that's the case the seemingly uncaring destruction of Metropolis and the killing of his enemy as shown in Man of Steel that did not sit well with many fans may well have been entirely deliberate...
:O
the basic plot of the new film could well be akin to:
the "proto" Justice League turns up in the wake of the last films events.
Superman is largely ignorant of them because "secrecy","coddling by the Kents" and/or "he's a country boy" and/or his time "avoiding the world" in the first movie.
"hey, you really should have kept a lid on some of that shit dude"
"why should i listen to you ?"
"because...I'm The Goddamn Batman!" <---i half expect this line to actually be said on screen btw
"..and if you're not prepared to you're a threat to all we hold dear"
"i have enough daddy issues and you're not the boss of me"
queue growling, the investigation of and potential deployment of anti-superman "stuff"
(the introduction of which may become important in later movies) and limited inter-superhero *biff* & *pow* etc
...meanwhile the new baddy "arises"...
"TIME OUT...hey guys...maybe we should really go fight this new baddy together hmm ?.." <-- a potential Wonder Woman line in the classic "too much testosterone in the room" tradition ?
"...ok...but don't think this means we are buddies"
*biff* *witty banter* *bonding* *pow* baddy defeated etc
"hey, maybe you guys are alright/right..."
Superman maybe makes some speech about what he's going to be and effectively commits to being "classic" "lawful good" Superman and a member of The Justice League.
*group hug*
Wonder Woman and Superman potentially have a little bit of "a thing" for each other by the end of the movie thus aiding Superman come to terms with his "i'm a lonely super being, no one really understands me" super-emo-ness
curtains...
in essence what you'd have is a classic Justice League line-up being formed due to conflict between an older and highly moralistic Batman and a younger "immature" "unbound" and potentially "dangerous" Superman.
if they pull it off...the introduction of the whole thing in one movie...and it will be a huge movie...they basically leapfrog all of The Avengers "stage 1" shenanigans and could go to straight into something akin to Marvels "stage 2".
its a high risk play tho and they are relying on the introduction of "iconic" characters with little exposition...but then The Avengers itself was written in that manner...seeing "stage 1" films was actually irrelevant to watching and enjoying The Avengers and entirely deliberately so...and i think that's DCs catchup angle here...