Personally I think this is harder than it looks. The recent rumours of Alberto Falcone seem very reasonable but I for some reason can't see this happening. I could see him as a recast Victor Zsasz who could be used in a more prominant role other than a none speaking role (Like Tim Booth's portrayal in Batman Begins). But Deadshot and Hush also seem possible given Levitt's recent portrayal in Inception.
Anyway vote and comment in the usual places!