We already know that Frank Miller is playing a big influence on this, which sucks, but whatever. So, the government (with Lex Luthor somehow involved) calls on Superman for a favor. Batman's busting heads in Gotham, nobody's above the law, only Superman can stop him, and you know, Frank Miller stuff. They fight. It's a big Hollywood fight scene and both hold their own, but Superman ultimately wins of course. Either he captures Batman, or Batman is injured and has to retreat, it doesn't matter.
But eventually Superman has a conversation with Batman, who reveals his problem with Superman. He explains how Superman can be something better. Something that Batman could never be. He can be this symbol of hope that the world needs, but instead he's wasting his potential by doing this whole brute force thing. Batman becomes the next influential figure in Superman's life, completing the man who Jor-El and Jonathan Kent started him out to become. Have Batman say something like "You can knock down a building. Let's see you stop one from falling." Something that really hits home what Superman was missing in Man of Steel, and cements what Snyder has been saying about him not really being Superman yet.
So something bad happens, Lex Luthor is a dick. Superman and Batman team up and stop the bad things. They part on good terms. Montage of people watching news footage of the destruction. We see Superman helping rebuild, and partaking in some boyscout stuff. We see kids putting on capes. There's a voice-over from somebody important. Doesn't really matter who. Could be Batman, could be Jor-El, could be Lois, actually Lois probably makes the most sense, since she's a reporter or whatever. They start talking about how real heroes inspire people. We see the aftermath of some robbery or something, as the police get there to find all of the criminals apprehended. They're confused as we see a woman walk by into an alleyway, wearing a trenchcoat, the sleeve of which pulls of just enough to see the shimmer of a gauntlet on her wrist. Cut to a guy about to be shot by a mugger only to be pulled out of the way before the bullet hits him and the mugger to be knocked unconscious by a red blur.
Voice-over says something optimistic, with the last word being "Justice." Credits.
Boom. Feel free to call me Goyer.