We have the 3rd Christopher Nolan Batman Film and the 1st Nolan supervised Superman film. As for batman I personally if I was a producer. Here is how I would plan things. After the 3rd film wraps things up plan for a new trilogy, if Nolan wants to work in it great, if not find someone would will give the directors chair to another director who can give the same gritty dark tone. Since the last trilogy was about the beginnings of the Caped Crusader, this trilogy should be about the origin of the Boy Wonder, Dick Grayson. The death of this family and Bruce Wayne adopting him and teaching him to fight crime. This 2nd trilogy could also introduce other villains such as The Penguin, Riddler and even since it will be a few years after Dark Knight, bring back the Joker.
As for Superman, this is going to be a young Superman at the start of his career at the Daily Planet, so first of all you do not need t show the destruction of krypton and his growing up in Smallville. Because everyone on earth knows the origin story of Superman, as as well as the story of Jesus Christ. We also had 10 season of that on the WB/CW.
Villans lay off on the Lex Luthor, we had 4 films with Lex and 1 with a knock-off imitation of him. He should be in this new film but as a small supporting background villian, maybe have in short scenes mentioning LEXCORP, and have him at the end in a scene showing how He was manipulating events from the comforts of his penthouse office. The villains should be something big, Brainiac, Darksied, something big and powerful that Supes and punch.
Maybe then work toward a Batman/Superman film.
That is how I would do things.