Copy paste from WoWHead (http://www.wowhead.com/weapon-illusions-guide):
"Weapon Illusions are a new transmog option for players in Legion. These illusions allow you to change the glow appearance of your weapon. Originally the glow effects were nice perks of enchants you applied to your weapon for stat boosts, but over time Blizzard has created Illusion versions of these Enchants. Now can use a current enchant on their weapon for stats, but modify the appearance of the glow for fashion."
I, personally, would love to see this on Warmane. It would also make Warmane make more money which is good? :)