Well, prayers have been answered it seems. From the preliminary patch 3.1 notes:

Items that dropped directly from boss enemies will now drop from treasure boxes in the following duties:
The Bowl of Embers (Extreme) / The Howling Eye (Extreme) / The Navel (Extreme) / Thornmarch (Extreme) / The Whorleater (Extreme) / The Striking Tree (Extreme) / Akh Afah Amphitheatre (Extreme)