The transmog system in wow limits you based on your class, so if you are a warrior you cannot transmog your armor to look like mail and cloth yet many cloth and mail armors look like plate...

Zos eso system really emphasizes the "play as you want" model so I can transmog my sorcerer to use full plate armor and look like a badass battlemage. Zos even will let you transmog your weapon of the same skillset to another (dw daggers to look like swords) and a step further they will make it so that you can dye your weapons purple if you wanted To. Bravo zos.

Some things wow does that Zos should do:
Unique quest reward items and dungeon reward item models you can transmog. Questing can be rewarding if you go back and give all the old models a unique model we can use for our outfits. Getting a sword from a long or even a god is lackluster when it's a basic Breton sword that you can craft.

Holiday transmogs: we have frostcaster and grim harlequin, how about giving pvpers some love and selling a motif similar to pelinal whitestrake's crusader gear? Also during witches festival have a scythe staff we can transmog drop

Holiday dyes: make them permanently buyable and applyable to transmogs

Unique items: expand and include lich, worm cult, and other unique non transmog items usable for transmog