Arrow and Flash have been confirmed to not be connected to the movies and the other shows, so that means that they might last a while longer (my logic there is because it is their own Universe, and can tell many stories on only two shows). The longer the time, the more characters to appear. I am sure Arrow will get at least to Season 5, so that gives much time for characters to appear. But who should appear?
My personal favorites would be Martian Manhunter, Stargirl, Wildcat, Hawkman, Riddler, Brick, and Plastic Man (OOH I Just love Plastic Man!).
Wildcat, Riddler, Brick, and Plastic Man could all easily work. Hawkman and Stargirl is getting trickier, and Martian Manhunter would be hard, but could work if puled off right.
Who would you like? And be real, the Trinity will not appear. Sound off in the comment section below!