One exciting storyline could be Superman Prime One Million teaming up with other powerful heroes from different universes to fight a cosmic threat that endangers all of existence. Maybe a villain has found a way to break through the barriers between universes and is causing chaos everywhere. Another could be a crossover where he meets a version of himself from a different timeline and they have to figure out how to merge their powers to save the day. And perhaps a story where he crosses over into a more magical universe and has to learn to use his powers in a completely different way to defeat a powerful sorcerer.
To create unique characters in this type of crossover, writers can play with the idea of power corruption. Imagine a character who starts off as a normal person in the other universe but then gets a taste of Superman Prime One Million's power and becomes corrupted. This character could then be a villain in the story. Another approach is to create a character who is a counterpart to Superman Prime One Million. They could have similar powers but a completely different upbringing and moral code. For example, a character who was raised in a world where power is used for personal gain and has to learn from Superman Prime One Million about using power for good. Writers can also create characters that are the result of a scientific experiment gone wrong in the crossover, combining elements of both universes in a strange and unpredictable way.
DC Comics has indeed taken this step. It's part of their effort to present more diverse and inclusive character portrayals in the modern comic landscape. This move aims to reflect the diversity of the real world and provide more representation for different identities within the superhero universe.
Superman is definitely a DC Comics character. DC has built a rich and extensive mythology around him over the years. He's a symbol of hope and justice in the DC world.