Press release says Cavill, Adams, Lane and Fishburne are confirmed to return and that a new Batman will be cast.
Here's the logo they showed at Comic-Con.
According to io9 Harry Lennix joined Snyder onstage for the annoucement and read the following dialogue:
I want you to remember, Clark… in all the years to come… in your most private moments… I want you to remember… my hand… at your throat… I want… you to remember… the one man who beat you.
It's from
The Dark Knight Returns. Snyder said the movie won't be an adaptation of it, but it'll be inspired by it.
Some quotes from David Goyer:
"We don't know what we're going to call it yet — 'Superman vs. Batman,' 'Batman vs. Superman,' — but those two guys on screen, that's happening."
"To a certain extent, Superman, cinematically, hadn't been reinvented since the Donner films. We will be dealing with it in the coming film. He's not fully formed in [Man of Steel]. He will have to deal with the repercussions in the next film."
Here's my premature theory:
In the aftermath of the Kryptonian attack on Earth, the US government contracts with LexCorp to rebuild Metropolis and with the newly solvent again (after Wayne recovered his fortune and the company got a bailout) Wayne Enterprises to develop countermeasures to fight any potential future Kryptonian threats. The government also does not fully trust Superman yet and is not sure whether he'll interfere with US government foreign policy, so secretly the project is also to develop countermeasures against him.
Wayne Enterprises has access to scans of Superman and Zod fighting in Metropolis and near their destroyed satellite, military scans of Clark's escape pod, Zod's Kryptonian armor which he shed in Metropolis, and the debris from the destroyed World Engine to analyze. They reverse engineer the armor and are able to access a Kryptonian computer from the world engine.
The Wayne Enterprises project is overseen by CEO Bruce Wayne, back from overseas and retired from crimefighting, leaving that to his protege John "Robin" Blake, the new Batman (Wayne is recast, and Blake doesn't even have to show up or can just be a brief cameo). Wayne has essentially taken over the trainer/mentor/armorer roles of Ducard, Alfred, and Fox from the DK trilogy with the rookie Batman Blake. Gotham is also undergoing its own recovery program post-Bane, allowing Wayne to fix the city's ills through charitable, social, and infrastructure/redevelopment projects like his father did. Bruce is content in this new role and is able to have a meaningful relationship with Selina.
Clark, through researching the Wayne Enterprises project as a journalist, learns of the nature of the secret program and its development of countermeasures against Kryptonians. Seeing as all the other Kryptonians are seemingly locked away in The Phantom Zone, Clark sees this as a clear threat to himself from the still somewhat distrustful US government and sees the potential for a new global arms race to develop using highly volatile Kryptonian technology that could destroy mankind. He vows to destroy the lab and all its data.
Wayne has anticipated this possibility though, and the lab utilizes Kryptonian materials in its construction, rendering Superman weakened when he lands there much as Kryptonite would. While Superman struggles to exit the lab, Bruce uses the time to prepare (

) by donning the new reverse engineered Kryptonian/Applied Sciences hybrid exo-skeleton BatSuit he was developing. This suit has sensors similar to Superman's senses, flight capability, super strength and speed, enhanced armor, anti-Kryptonian weapons, and can survive in most environments, including space. It's an improvement on the Kryptonian armor which Zod and Co. were able to give Superman a very hard time dealing with.
Superman and Bruce/Batman fight to a draw after an epic battle that leaves most of the lab destroyed anyway, with the exception of the suit. Unbeknownst to Clark and Bruce, their fight has lowered containment protocols around the damaged central computer of the world engine, allowing the Kryptonian AI Brainiac to escape into Wayne Enterprises computers and eventually into the wild. When Clark and Bruce learn of this, they decide to set aside their differences and team up to stop Brainiac before it can gain control of the US military's drones, ships, nuclear stockpile, and other automated systems and threaten the world. They have another epic showdown against Brainiac's armies of robots and vessels, and eventually emerge victorious together.
Clark decides he can trust Bruce with his secret identity and with the ability to kill him and other Kryptonians with Kryptonite should something go wrong with him. Bruce shares his identity with Clark as well, and decides that he's not ready to give up the mantle of the Bat just yet, vowing to fight to change/save the world from the bigger threats it faces while letting Blake deal with saving Gotham. As far as the people know, though, both Batmen are one and the same person. Clark and Bruce also decide that they need to form a team to counter threats to the Earth, thus leading to the Justice League.
In the coda, Bruce tells the US government that he will no longer be developing the Anti-Kryptonian weapons that he promised them, seeing the project as a dead end with no applications. The US government is not pleased, and decides to take what materials and data they can salvage from the Wayne Enterprises lab and bring it to the next interested party, LexCorp. As the films ends, we see greedy corporate CEO Lex Luthor looking over the tech and smiling as he contemplates what he can do with all of this power. In the background, we see campaign mockups promoting Lex Luthor for President, which is his next step after becoming the billionaire hero who spent a fortune rebuilding Metropolis.