I thought they said something about unlocking essences for other roles if your main met the requirements in the initial announcement… I’m gonna go check.
*edit:
Looks like just the Mechagon and Nazjatar ones should be unlocked regardless of your role assuming they stuck to this initial plan.
Okay just checked on my Paladin alt after logging into this Shaman and I can buy the tank essences from Mechagon and Nazjatar on my Paladin.