Nightwing is the perfect film to right the DCEU ship.
It basically writes itself. For starters, flashbacks to his time as Robin humanize Batman and add crucial context to his descent into a crazed killer. There's a clear and compelling reason for Dick and Bruce to be estranged. Dick provides a natural way for the tone to shift away from that of BVS without feeling forced or artificial.
A while back I said that the DCEU should have started with a Robin origin story where Dick (rather than batman) is the point-of-view character. Obviously the ship has sailed on that, but a Nightwing film provides a lot of the same advantages. In particular, Dick Grayson can easily be positioned as a linchpin figure connected to many parts of the DCEU (the way Iron Man was positioned in the MCU).
Frankly, I believe wholeheartedly that what the Batman film franchise desperately needs to reinvigorate itself and re-engage with audiences is a batman & Robin film... but this is the next best thing. I was actually just saying to a friend the other day that the batfamily is it's own fully-functional cinematic universe and that WB would be stupid not to capitalize on it.
I hope to hell it's good (or actually happens at all), because if they squander this opportunity, that would just be sad.