Agreed in a mmo tbh in modern times a transmog sistem became esencial and fundemental, that why detsiny 2 added transmog and under free but time locked methods and also pay methods, the same as wow, dc universe, trove, guldwars, pretty much mmo always have a transmog heck even minecraft with skins, and tbh teh highest content in minecraft from the comunity is skins, and the store gives you free skins, and threw earning certain achivment yo also unlock some skins, or compleating certain dungeons, quest and achivment like The Eldercrolls online.
pretty much big mmos have tansmog and free options to players i really enjoyed the methode Eso did it becuse it had a lot of free mthods to get them be it: achivments, limited event, dungeon drops, world drops, special books called montiff that gave styles, compleating certain dungeon, finishng certain quest the lis goes on and on, and on the start people also got free starter apearences.
if you whant your mmo to survive and i mean highly chance too almost gareenteed, that this has been true to all game i mention above including non memmo like teraria with vanity, or minecraft and other similiar games witch skin, or dersser etc. you nee transmog and method to get free transmog.
if their anothing a player whant to be in a mmo its being themselves and feeling like themselves and having transmog give a extreme amount of reputation to the devs from the player im serious, even darksouls had a sence of tranmog since amor worked more for poise then actual damage resistance so it was a inderect cosmetical thign were you can use anythign you whant and how you whant to loock with afecting minimal gameplay.
if there somthign that makes money in mmo and never fails and brings atention of a lot of layers, is variety and quality of that variety.
and being able to look how you whant with multiple options and not so tedius like the dye sistem in this game tbh, is a greta huge impact to the player and give a lot of variety, and Uniqueness/ FREE PLAYER CHOICE.