For those who haven't seen this, note this is an artist's speculations and not mine
Caithe in the book is a classic Assassin which would be the figure above the Necromancer. The second from the right (purple lady) would be the Mesmer making their return (also mentioned in the book.) That leaves the Gun wielding Charr. Since a gun only class has been confirmed (as in not bows but still melee weapons) my guess is Corsair or Privateer.
Weapon set is; Main: Sword, Axe, Pistol. Offhand: Torch, Warhorn, Dagger, Pistol. Two-Hand: Rifle
The only problem is that I can't think of a mechanic for them. Assassin would have an active stealth in PvE while out of combat to bypass mobs unless close, Mesmer would have illusion based mechanic. None of the other classes have overlapping mechanics so if we can figure out what it might be, then we might have a basis for it.

Caithe in the book is a classic Assassin which would be the figure above the Necromancer. The second from the right (purple lady) would be the Mesmer making their return (also mentioned in the book.) That leaves the Gun wielding Charr. Since a gun only class has been confirmed (as in not bows but still melee weapons) my guess is Corsair or Privateer.
Weapon set is; Main: Sword, Axe, Pistol. Offhand: Torch, Warhorn, Dagger, Pistol. Two-Hand: Rifle
The only problem is that I can't think of a mechanic for them. Assassin would have an active stealth in PvE while out of combat to bypass mobs unless close, Mesmer would have illusion based mechanic. None of the other classes have overlapping mechanics so if we can figure out what it might be, then we might have a basis for it.