The items:
Neltharion himself:
Wowhead says its plate, even though I don’t think the actual item has been datamined.
My money is it being mail, completing the Archimonde (cloth) / Xavius (leather) / Garrosh (plate) trend with some Evoker stuff with Hunters and Shamans tagging along.
I think the best solution is cosmetic, however.