My list is a freaking Christmas List! Off the top of my head:
1. A scene of Bruce Wayne training in the Batcave, honing his fighting skills as he casually converses with Alfred.
2. A scene with Lois and Martha. Martha perhaps visiting Metropolis to get a better handle on this woman that her son so obviously is smitten with.
3. Batman confronting Superman on MULTIPLE occasions and frankly, totally whiffing on his first try, but learning valuable information in the process. Conversely, Superman should be incredibly impressed after that first try that a mere human actually escaped from him to fight another day.
4. A scene showing how Lex Luthor is a semi-beloved and venerated figure in the wider world. He's held in high esteem by many, especially among his employees at Lexcorp.
5. A scene of Batman facing a physical opponent that is his match, on a Deathstroke or KGBeast level, especially if it occurs after we see him capable of just walking through like a room of regular thugs and goons.
6. A huge set piece of Superman trying to handle a big natural disaster of some kind, possibly with complications thrown into the mix by Lex.
7. Above all... MUTUAL RESPECT that could easily lead to friendship between our two heroes. I don't want the usual Batman passive aggressive bovine excrement. Once he knows something of Superman's true nature he can't treat him (or other members of the League) like idiots, fools, or children. That crap got old real fast in comics and toons.
8. A moment between Batman/Bruce and Martha Kent where she dresses him down in some way, and Bruce simply replies, "You know... My mother's name was Martha too."
9. A moment where Lex thinks he has Batman at his mercy, and Lex fires some kind of gun or rocket missile straight at him. Batman gets hit. Lex celebrates... Only to have him get up and we see a smoldering hole in the Batsuit... behind which is the S shield.
