Here's some more speculation while we wait for the next character reveals. The Aquaman trailer from a few weeks back offers a brief glimpse at a character who has seemingly yet to be revealed:
http://i.imgur.com/vzOQlSF.png
Shazam is the only other caped character we know of, and it doesn't look anything like him to me
Costume 1
Costume 2
It must be Black Adam or Martian Manhunter, but Black Adam wears long black sleeves (we've already seen
his character model), and this mystery character appears shirtless. He also looks to have the "underwear over tights" thing that Manhunter has going on. I don't know. What would Black Adam be doing with Superman, Green Lantern, and Hawkgirl, anyway? He's one of DC's most ruthless villains.