5. Change Batman's Story
This could be a very interesting one. We know most of the big events that happened in Batman's story, how certain events affected him and his friends, and in some cases how the whole city changed because of some incidents. But haven't you wondered what would have happened if some character did something different? Or than instead of some event happening something completely different occurred in some other place? Doing something like this would be very hard to pull off because some fans might not be pleased with the alternative stories that could be unfolded with the choices you make, or the criticism might come from how unsatisfying some people felt one of the endings was. However, that's a risk every company makes while doing a game with alternative endings, and just like those games, it would motive players to unlock different endings. It could be made like one of those "choose your own story" books, letting you make different choices while reliving different stories (like The Dark Knight Returns or The Killing Joke) and experiencing the consequences of said choices and how much it changed things. Something like this might be very complex, but I think it would be fascinating to see how much Batman's life would have changed if he did something different.