5) Superboy
Like most DC Comics characters, there have been many different versions of Superboy over the years. Some have been younger versions of Clark Kent, while others have been clones or hailed from alternate realities, but utilizing this character in the movie could work really well (especially with rumours of Cyborg solo outing becoming a Teen Titans spinoff).
[zergpaid]Seeing as Lex Luthor will be playing around with the corpse of General Zod in Batman V Superman: Dawn of Justice, the Kon-El/Connor Kent version –  who was a hybrid of Lex ad Clark’s human/Kryptonian cloned DNA and created to be the ultimate living weapon – would perhaps work best. It would also shake up Superman’s life in a big way, especially if he has to take this youngster under his wing.