8 Reasons Why Superman Should Be In Shazam!
2. Lessons Learned
Going right alongside the fact that Superman is Billy's idol who inspires him to become a hero, is the kind of moral lesson that Superman could teach the boy.
Obviously, a ten-year-old boy getting his wish granted and suddenly obtaining the powers of a superhero is going to have a lot to learn, even with his untold wisdom. Having Billy come face-to-face with his idol and realize that being a superhero isn't as simple as he had thought it would be would be a quick and incredibly effective character arc for both Billy and Superman.
It would allow Billy to continue learning from his idol and realize the real-world consequences of his dreams and aspirations, while also allowing Cavill's Superman to transition into a more nurturing mentorship-style role. In previous films, Batman and Wonder Woman had both already been superhero-ing about for years prior to their introductions. But Superman was a character whose origin story was shown to us in great detail and as a result, has always been the youngest and least mentor-like of the core three.
This transition could easily be made here and give Cavill a chance to even begin to pass the torch on to the next generation of DCEU stars in a graceful and appropriate way that still allows him to stay onboard. It's a win-win.