My guess at the 5
Dragon Born Fighter
Eladrin Wizard
Dwarven Cleric
Human or Halfling Rogue
Tiefling Warlock
I think that one poster is right that they will want to show off the new races of DragonBorn , Tiefling, and Eladrin. I think the 5 classes are the ones that are "done" in Races and Classes which were Fighter, Cleric, Wizard, Rogue, and Warlock.
DragonBorn Looks like a good fighter or leader class so it could swap with the dwarven Cleric to fighter. Eladrin seem to be made for the wizard class, and tieflings seem taylored out for warlock. That just leaves the rogue who could be any of a number, but I would bet on a least one human, but halflings also got a face lift. I also think the party composition will be :
Defender
Leader
Controller
Striker 1
Striker 2
But I am just guessing. I would bet the module is already at the printer so to speak. I wish this was coming out sooner, and I believe that this is a marketing mistake. Ian.