Injustice: Gods Among Us demo is live on PSN and Xbox Live, the game's associated Avatar goodies have also hit the Xbox Live Marketplace. Of the many offerings available (Wonder Woman/Superman/Batman logo shirts, etc), the costumes for Killer Frost and Ares seen above are by far the most interesting, since those characters haven't been announced for the game.
Considering that every other available costume is for one of the game's many playable characters, we feel safe in assuming that Ares and Killer Frost haven't been thrown in for giggles. More likely, these two villains are either unlockable fighters, or future DLC. We've reached out to NetherRealm studios for more information and will update with anything we learn.