I was just thinking about this.
The DC Extended Universe is now a thing, officially, thanks to the success of Wonder Woman. Does that mean it will be good moving forward? Fuck no, but it means that they'll commit to this post Justice League, and in a big way, at least until a Wonder Woman sequel flops.
So, Robin. Assuming we're still getting a solo Batman movie, there's hope for the greatest sidekick in all of comicdom to finally make a proper, respectful appearance.
Here's a list of prospective castings and angles.
Many people think that the way the DCEU is set up, there's already been a Dick Grayson and a Jason Todd. This would be awesome, because then you can easily dive into some Nightwing, some Tim Drake, and some Red Hood.
So, first off, I think of Logan Lerman. I think he'd be a great Tim Drake. Also, there's this dude Dylan Minette who could totally pull it off. But you could go geekier with Tim, so the sky's the limit for young talent out there.
As for Nightwing, my mind always goes to Matt Bomer. He works especially well in this universe where Batman is older. Adam Driver has been rumored, and that would be ridiculous and amazing, but I don't see it happening. Unless it was a solo Nightwing project that he could sink his insane acting chops into.
You could also totally pull of a female Robin in this universe. Already Jena Malone was rumored to be Carrie Kelly, but they could go Stephanie Brown easily, maybe even with someone older. My mind goes to Ana de Armas, though she's perhaps a bit too old. I think she can play it younger, though, and she's got a great look for the Snyder-verse.Of course Anna Kendrik's name gets tossed around for all this shit, from Squirrel Girl to Batgirl, and so I could see them wanting to work her in. Oh, and another of my faves who doesn't get enough play is Teresa Palmer. She could totally be Spoiler/Robin/Batgirl. (Also too old? Maybe?)
Of course they could skip over the rest and go straight to Damian Wayne. That casting is impossible, because there's no way they'll bank on some actual little dude. They'll probably grow him up, and then who know what he'll look like?
Short Answer: Some other randos for Robin or Nightwing include: Dave Franco, Zac Effron, and the oft-mention Joseph Gordon-Levitt, though fuck that last one. He was already Batman. He was. If you didn't get that, you're dumb.