Players noticed a distinct lack of 
Stygian Stones on the 2.0 Public Test Realm. Endgame bosses were being summoned without the material. The PTR being the PTR, some were unsure of whether this was actually happening in the full release or not. Luckily, we got an official response today.
Recently promoted Global Director of Community Adam Fletcher confirmed that the stones are a thing of the past in 2.0, and also revealed that existing ones would be turned into a “significant” amount of gold.
This will make summoning bosses easier, which is always a good thing. We can’t wait for the expansion to arrive, and we’re only two weeks away! You can check out all out Vessel of Hatred guides here.