When I made my 2.5 Class Sets topic, which you can preview here: 2.5 Class Set topic, my work around for IK Maul was changing the Indestructible mod to Self Repair(1 Durability every 4 seconds). As it stands, if something is inherently Indestructible, it can never roll Ethereal unless it ROLLS Ethereal all the time like Shadow Killer Battle Cestus for example.
Another idea I had floating around in my mind was to change Anya’s quest reward after killing Nihlathak from personalizing an item to adding Ethereal modifier to any given item, even one that is Indestructible(Bows/Crossbows would obviously be exempt unless you want to change that?). Meaning, Normal, Rare, Magic, Unique and even Set items would apply(So you can get Ethereal Aldur Boots, Ethereal IK Maul, etc.). Granted I’d love for Ethereal flag to roll on Set Items to begin with but it’d be a way to ensure getting Ethereal items for your characters without having to painstakingly hope an Ethereal flag rolls on X item. Other idea I had for her quest was to have her add/change Staff Mods but I think the Ethereal reward would instantly make A5 Q4 a given to be completed due to how valuable Ethereal modifier is on items.