Buried deep below the Wowhead Shadowlands Pre-Patch Build 35917 spell changes, I noticed that many of the Warlords of Draenor essence consumibles to improve the crafted gear using the BoP materials have become grey quality (EDIT: THEY CANT BE USED IN THE PTR AND SELL FOR 0c) and the associated spells in the profession tab have been moved to Uncategorized (AKA, removed).
The reasons why Blizzard has decided to do this, in my speculation, is to remove any unintended behaviour with the Relic of the Past V applied to WoD crafted gear and the essence ilvl upgrade. As a collateral damage, this means that the transmog for upgrading WoD weapons and armor sets will be no longer obtainable when prepatch hits live servers.
In case you are unaware on how this system works, WoD crafted gear had 6 possible upgrades, using consumible items (named essences) to improve the ilvl of the item. Some unique appearances were locked behind Stage 2 and Stage 3 of the item. If this change is final and WoD essences are removed from the game, Stage 2 and Stage 3 appaearances will be, effectively, unobtainable in Shadowlands.
Some interesting links: https://ptr.wowhead.com/item=128015/truesteel-essence
, grey quality. https://ptr.wowhead.com/item=128016/steelforged-essence
, grey quality. https://ptr.wowhead.com/item=128014/burnished-essence
You can see the armor sets and appearances of the weapons here. Leatherworking, Tailoring and Inscription also have unique appearances.
Personally I bought every Sorcerous Earth and Huge Ogre Cache for work orders to prepare for this change as I want the transmog before it leaves the game.
It can change before it hit Live Servers but I doubt it.TL,DR: WoD upgrading items are no more in the PTR. This change will make related upgraded items transmog unobtainable.