7. Nightwing
Putting Robin in any future Batman movie is going to be a bit of a challenge for two reasons: a) Batman and Robin made the character a complete joke and b) even with a great script, it's difficult for a Batman-Robin partnership not to devolve into some sort of camp and/or gay joke. That's why it would be refreshing to see Robin replaced with Nightwing, the later identity assumed by Dick Grayson, and a part that has already been rumoured to be a part of Batman vs. Superman, with actors such as Adam Driver and Ezra Miller being linked to the part.
The Cameo: Given that the movie will be dealing with a semi-retired Batman, and Latino Review claims that an early draft of the script mentions Bruce Wayne falling out with Dick, it would make sense for Grayson to show up in some capacity, perhaps being the man to help bring Wayne back into the fold? Granted, it would be a challenge to fashion a cameo role for the character that still gets him in his Nightwing suit, but he could make a brief appearance to bail Batman out at a crucial point in the movie, ahead of preparing for the final battle?