If the project makes it to the big screen, you might assume that Dick Grayson will just be a new addition to the universe, but that might not be the case.
Batman V Superman: Dawn of Justice established early on that there was a previous Robin. In Batman's Batcave a display case can be seen with the older style Robin suit, which carries a spraypainted message from the Joker. Joker and Harley had a hand in killing the boy wonder, and DC has essentially confirmed that it is indeed Jason Todd. If the timeline follows the comics, however, that means Todd is not the original Robin, and with Bruce being older in the films, it would stand to reason that Dick Grayson already exists in the Cinematic Universe.
Batman nor Alfred mention Grayson by name in Batman v Superman, but there could always be a tease in the upcoming Justice League. Following the comics timeline, Nightwing would have pursued a leadership position amongst the Teen Titans, and eventually, touches down in Bludhaven as his city of choice. This would be an easy way to bring the character right in, essentially having him return to Gotham after a long absence.
There is thinking that this could be the first step in getting Affleck out of the Batman role. In the comics, there was a point in time where Batman was thought dead, and Grayson took over the mantle of Batman in his stead. He adopted a tweaked costume and Damian Wayne as Robin in his effort to carry on the title, but eventually, Bruce returned to reclaim the role. That could essentially be the storyline here, with Grayson replacing Bruce and allowing a younger actor to take on the part, giving Affleck an out.
All Warner Bros. would need to do to make this work introduces the character in Matt Reeve's upcoming Batman solo film (currently sitting at a 4.18 out of 5 on ComicBook.com's anticipation rankings), paving the way for Affleck's exit down the line.