2) Bizarro
Literally the anti-Superman, Bizarro is one of the Man of Steel’s oldest foes and has been continually revised over the years – which means there would be lot of ripe material for Man of Steel 2 to mine.
Traditionally, Bizarro is an alternate version of Superman from the Bizarro dimension where everything is the exact opposite from the regular universe. For instance, the reverse S emblem on his chest.
While that rendition would be too goofy for the DCEU, there is a lot of potential to do a modern incarnation of the character. Maybe Lex Luthor refines his Doomsday project and makes a clone of Superman? This Bizarro could be presented as a tragic Frankenstein’s monster type who, like the real Superman, would be the only one of his kind.
All right, maybe that would stray a little too close to Superman IV: The Quest for Peace, but the idea could still have legs.