That terrible thug saved the earth and spent many offscreen instances saving lives. But nah, a cameo from Nightwing would derail MOS2/Superman-Batman like a Hawkeye cameo derailed Thor
1. There is a considerable difference between Grayson and Hawkeye. Grayson is the most prominent of the two and well to known audiences. thanks to heavy exposure over the past few decades (Batman 1966, Batman Forever, Batman: TAS, and so on); before the Avengers, Hawkeye was not. His screen coverage was limited in Thor; if the Avengers was not made, he would be not be remembered as fully.
2. My second point feeds from this: with a prolific character such as Grayson, a cameo would not occur. He would become a supporting player in the film's narrative. I seriously doubt DC would keep Grayson on the sidelines of the action of Batman versus Superman. Hence, they would keep him in the narrative, which would eat up even more of screentime that should be allocated to Superman.
3. There has been a progression of reducing the screentime for Superman. First, the film project was MOS 2. Then, it became Batman and Superman, which reduced 50% of the narrative focus/screentime that should be allocated to him. If they follow the traditional model for a vs film - and which they should, since they are resurrecting a novelty in storytelling (name on good versus film. There are none)-it equates to each character getting around 50% of the screentime, unless they try the format of AVP/FVJ, which they have no need to, since it is not a horror film.
4. I have a different aesthetic on violence in superhero films than David Goyer. While he is a is a wonderful writer, he sees killing as the only way to stop supervillains. In the case of Batman, he wriggled around and had Batman create circumstances that caused the death of characters - leaving R'as to die on the train, knocking Dent off the building, and so on-with the exception of Talia. Okay, whatever.
But Superman, who has god-like power has no need to kill. As Superman vs the Elite showed, there are alternative ways to dispatch villains without snapping their freaking necks. Part of the reason I was hoping the project was going to be a Man of Steel sequel was because I was hoping they would follow a trajectory similar to Arrow: have the character relinquish his murderous impulses and become an elightened, idealized hero. However, since they decided to sacrifice it for currently looks like a 1950's B-film slugfest, it seems unlikely they will follow the trajectory.
