To put that in perspective, the high-priced vanity mount released with Legion is a giant spider called the Bloodfang Widow. It costs 2 million gold. If you wanted to buy one with cash, using WoW tokens, it would have cost over $1,100 at the time Legion was released, in August 2016. If you wanted to do the same thing in July 2018, it would have cost less than $200.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.