I think Bats is uniquely qualified to help Supes deal with the moral issues of justice versus revenge. Bats has had to come to terms with the "no killing" code he follows and will probably be able to mentor Supes in a way that no other human could. It would be interesting to see Supes learn from the example Bats sets for himself.
Just had to comment on this part here. This is exactly what John Byrne did when he wrote the post Crisis origin of Superman. That was the origin that DC used for years (occasionally tweaked during things like Zero Hour, but essentionally it was the origin used by writers up until post 52). In the origin Batman had already been operating in Gotham for a while and Supes was just getting started. People knew about Superman, but he wasn't the hero's hero yet.
Batman had come to Metropolis on the trail of some criminal, and of course Superman had to check into this guy showing up, beating up seemingly random people, and stringing them up on street lights. After the usual superhero misunderstanding fight they start to work together. In the end it ends up with Batman leaving, acknowleging that Superman is a legit hero and Supes coming away knowing that there are others out there doing good because its the right thing to do. And an appreciation of what humans are capable of. Its the idea that the 'hero' isn't actually a Hero until acknowledged by an older/established hero.
It also had the great moment of Batman, after realizing that a thug lied to him during an interrogation goes, "him, seems he's more afraid of her than he is of me. Shame really. He's such an athletic kind of guy, he's really going to hate spending the next few months with two broken legs.". An Superman's astonishment that Bats would even think of doing something like that
