The outfit system as it is now is quite good. Besides the cosmetic changes it brings, I like that it gives further value to crafting styles, and rewards the people who invest effort in getting them.

However, there are some limitations that I do not understand, like not being able to hide shoulders/gloves/belts/etc, or using other type of gear for further customization.

(I know this has been asked many times, but I want to give a reason why I want this) Please add the option to hide shoulders/gloves/belts, maybe even chests or boots.
The reason for this is that some people like to play a mage/healer/thief or some odd character that does not wear a lot of armour.
Have you seen any movie with a vampire wearing shoulder caps or large metal hip flaps?
Also, there are many situations where players might want to role play.. or just to have fun creating NPC outfits: fisherman, blacksmith, merchant, beggar, brawler, etc.

An other suggestion is to be able to unlock NPC clothing in the outfit system, by finding and looting it from wardrobes or baskets. The current list of looted clothing could be expanded to include rare or very rare clothing like the armour used by some key NPCs. This could open interesting possibilities, new achievements and stuff to collect.

You could also add the current costumes (disguises) used in quests to the outfit system, after the quest is completed, so we don't have to keep favourite disguises in the bag.