Interesting thought exercise.
What if Batman/Superman went a very different direction? I know that's not a unique exercise, even here. But I was thinking about it, and I think they could've done a story that's unique to both characters on film. It's way different than what we got, but I think it plays with a bunch of the same themes.
Opening plays out the same way. Batman sees what happened in Metropolis and is super angry. Locates the kryptonite and attacks in the first act of the movie. Clark has been working around the clock to save people, fix his image, etc, and he's caught completely off guard. They fight for a bit and (insert comic technobabble/magic/whatever), something happens and both heroes are shot backwards.
Clark moves to continue the attack. Batman steps back in a defensive manner. Clark stays where he is. Batman ends up in the middle of nowhere. For whatever reason, Batman is now superhuman and Clark isn't.
So you have Clark Kent now what he's always wanted to be - normal. Not only that, but he has this giant weight lifted off him - he's not responsible for everyone anymore. He can't hear the screams anymore, and he doesn't feel obligated to try and save everyone. He's still fascinated by what happened, but he has no idea who the Batman is. He has no idea how the change happened. He lets himself enjoy the moment - he goes back to work and goes back to Lois.
Bruce, meanwhile, is flipping out. Now *he's* the alien? He went up against the alien and won. Not only did he remove the threat, but now the power is in *the right hands*. And, yeah, he's struggling with controlling *any* of his powers, but he's Batman. He'll mediate and do tai chi and figure it out.
I just came up with this in the last few minutes so it's not refined, and I don't really have a 2nd/3rd act. I'm sure Batman would lose control and mess something up when he was trying to fight crime. And Clark would use his journalism skills to figure out what happened and who Batman is and work to get his powers back after he realizes Batman can't handle them.
But by the end of the movie, Batman would understand what Superman was all about. He'd know that he's not some crazy alien - that he used his power responsibly and did it better than Batman ever could. We'd get to see a human side of Clark because that's all there'd be.
And if you ended with Clark's sacrifice, I think it sets up the same way. Clark's gone, and Batman feels this great pressure to honor him. And he's had this great power, and now he has to assemble the Justice League because he *knows* he isn't enough to fight all the darkness.
I know that's the kind of movie that Hollywood wouldn't make, but I think it would've been a more natural sequel to Man of Steel (Clark, having accepted himself, now gets what he thought he always wanted) and gives us a different take on Batman who now understands where this part of his life needs to take him.
Not meant to be a criticism of BvS (I'm still in BvS jail) - just an idea I had all of the sudden this morning.