I can't believe that they would waste this much time on "Robin" if the character wasn't being setup for a spin-off series. Given the popularity of John Blake, I'm sure we'll get a Nightwing movie in a few years.
I doubt that. It would de facto be a fourth Nolanverse movie, and I think it was made perfectly clear that it ended with part three.
But the question is, if WB were to get greedy and decide to profit on nu-Robins's popularity (which could end up being short lived, it's too early to tell), would they even get JGL to play him again? Nolan's actors are known to be pretty loyal to him, no? And as far as Nolan is concerned, this thing is definitely over.
Nolan doesn't own anything - Warner's does. If they want to make a movie that is essentially a continuation of this unvierse there's not a damn thing Nolan can do to stop them. And why would he care if they did? He's moved on to other projects. Everyone keeps talking like Warner's is going to be tiptoeing around Nolan over these movies and this universe, which isn't exactly how studios operate, especially with as lucrative of a franchise as Batman.
As for whether they could get JGL - he's plainly positioning himself as an action leading man right now (Premium Rush
due out in a couple of weeks), and a Batman II sequel would probably be a big ticket item for at least one film. Blake's story was by far the most interesting character piece of the film and there is a lot of buzz around it. You never know. I imagine it would depend on if they could get a workable script.