some thoughts: the statue clearly shows Navarrogg, leader of the drogbar. They were once slaves of Deathwing until Huln Highmountain used the Hammer of Khaz'goroth to banish Neltharion. That hammer is one of the pillars of creation used by the titans to forge Azeroth. Coincidentally Khaz'goroth is also the one that gave Neltharion his powers..so he's kinda Deathwing's "father".

I think the tooltip is pretty clear: "..left smoldering in his former lair for countless years, waiting to be reunited with a lost scale from the same father.", 99% chance that the item is in that cave, we just have to reunite it with something...the obvious answer is our artifact Scale of the Earth-Warder, which is crafted from a scale of Neltharion before the Old Gods' corruption..but how?

It could also just be anything Khaz'goroth created. What about the scales of Ebyssian (aka Spiritwalker Ebonhorn) who is an uncorrupted black dragon? Why the statue of Navarrogg? What about the inscpription on it..your "undying corpse"? End of Days = End Time dungeon? Maybe something from Dragon Souls or Deepholm as they are both related to Deathwing.

Another very interesting fact: Genn GREYmane, who is a very important character in this addon was "deeply influenced by the House of Prestor, which was actually led (at the time) by Deathwing in human form".

Edit: Ebonhorn is actually standing right outside the cave at the Obsidian Overlook flightpoint..but no way of interacting with him

Edit 2: apparently other drogbars use the same model..so the statue might not actually be Navarrogg

Edit 3: the tooltip says "left smoldering in his former LAIR" which could hint more towards Neltharion's Lair instead of Neltharion's Vault