With characters like Firestorm and The Atom coming to The Flash and Arrow respectively, some fans have started to wonder whether we might get more big-name DC crossovers on the hit CW series.
While they didn't slam the door on any major DC characters showing up, producers at last night's Flash Vs. Arrow fan screening (they in fact screened both The Flash episode "Flash vs. Arrow" and the Arrow episode "The Brave and the Bold") did single out Gotham City and Metropolis as being off-limits to their shared universe.
"There are things we can do, and there are things we can't," said executive producer Andrew Kreisberg. "I'm a huge fan of Nightwing. But there are cities we can use, and then there's everything else. You won't be hearing Gotham or Metropolis on the show anytime soon."
Of course, Bludhaven -- where Nightwing often operates -- has been referenced repeatedly on Arrow.
Certainly the success of the shows -- nobody seriously believes that they won't both be back next year, even if they haven't officially been renewed -- and the fact that they exist in a universe that isn't shared with Gotham or the burgeoning "DC Cinematic Universe" has helped; at Comic Con this summer, producers acknowledged that they were being allowed to do things and use characters in Season Three of Arrow that would have been verboten in Season One. But there are still some things where they aren't quite there yet.