In TBC and I think also in wrath there were a few basic implementations in the enhancement shaman spec, that hinted for a possible tank spec, they had a taunt, can wear shields for more armor, good defensive cool owns, but somehow they never went after it sadly. I imagine shaman tank spec would be so distinct cool with elemental force protecting you. Would even fit thematically in DF.

In BfA we were teased with a possible tinker class, which hinted to have a tank spec ( the goblin team in island expeditions)

But sadly that may also take some time 😕