I think it will be some type of job that transforms into another creature during combat such as Mutant or Druid. A major theme of the expansion is nature and the shirt says Mutant Mayhem, and turtles also are mutants, morphed from their original form, which hints at the idea of animal transformation.

The expansion also involves an civilization based on Mesoamerican civilizations like the Aztecs who had Jaguar and Eagle Warriors, which further hints at an animal transformation theme.

Green is typically a color associated with druids in fantasy. Druids often are depicted as transforming into bears. Viking berserkers were also said to transform into bears in battle.

Therefore, the new melee dps job will be Mutant/Druid/Berserker and will be able to shift into animal form.