This immediately causes gameplay concerns.
If this is truly going to be a PvP focused game, part of that means gear and abilities need to be recognizable.
If you can't tell what the heck is going on, you don't have a good PvP game.
League of Legends can have this - because it doesn't have items that impact how a character looks. The "costume" of the character, per se, is completely cosmetic. While in a game like World of Warcraft, Albion Online, etc.. you can discern what a player's power level is by looking at them. This is imperative, if you're going to make a decision to engage, or disengage. Who to target first, etc.
Having skins in an MMO like this lowers the skill bar.