6) Tim Drake (Robin/Red Robin)
Grayson might have been the first Robin, but he was definitely not the last. Since he vacated the position, Batman has recruited numerous orphan children to become his students in the subtle art of ass-kicking while wearing tights. One of the most popular and prominent is Tim Drake, the third Robin.
Assuming that the comic book chronology is still the same in the DCEU, then Drake could be the current Robin by the point the movie is set (that is, if Batman picks up a new sidekick sometime in between this and Justice League). It could be fun, then, to pair up the angsty, hardened ex-Robin with the younger, more naive current Robin. Fans of The New Batman Adventures animated series will be familiar with how well Nightwing and Drake’s Robin bounce off each other.
Alternatively, Drake grows up to take on his own breakaway vigilante in the comics – Red Robin. The Nightwing movie could bring both of Batman’s ex-sidekicks together and possibly examine the lasting effect that being trained by the Dark Knight has on a young boy.