6. Lex Luthor, President
Lex Luthor won't be the President of the United States when he's introduced in Batman v Superman: Dawn of Justice, but including some sort of reference to his potential future political aspirations is a must. It played a huge part in Jeph Loeb's well-received Batman/Superman series, and is a storyline which has all the makings of a great Man of Steel 2. Hell, why not a second Batman v Superman movie somewhere down the line? Jesse Eisenberg's take on this iconic villain is still very much a mystery, but various set reports and rumours have indicated that he will be rubbing shoulders with Senators and the like as part of his anti-Superman stance while also helping to rebuild Metropolis. Putting the villain behind bars at the end of Batman v Superman would limit what could be done with him in future, so an Easter Egg teasing what might be to come for Lex is the way to go.