But Young Justice isn't exactly Teen Titans, so they may not go with just the TT heavies. Dr. Light seems like a good guess, but I suspect it's a looser collection of villains. I'm a huge Legion of Doom fan though and I hope Black Manta is in there somewhere.
Also, do we all assume that was Artemis's arrow and not Speedy/Arsenol's? She's taking a while to show up is all.