Assuming they were inclined to do a Robin film, would "Robin and Batman" be worthy of adapting? It looks good but I'm trade waiting most of my books these days and haven't read it yet.
In any case, I'd be fine with a "Robin to Nightwing" evolution over the course of several films, but I don't believe DC/WB have the talent, skill, or patience to pull it off. And because most/many of their films aren't that good (by my subjective standards at least) I'm in no rush to see them try anything with Grayson at all.
But I don't think he'd be a hard character to get right in film (WB probably wouldn't manage it, but it doesn't seem difficult). The role and concept of Robin is so deeply engrained in pop culture you don't even need a film or three with Dick as Robin before going into Nightwing, you could just establish his past as Robin in the first Act and move on. Establish in all the trailers that this is Robin grown up and you benefit from the name recognition of Robin without having to spend much time with it.