The appearance button on the jewelry bar seems pretty useless outside of single player.
If that button when clicked showed a list of sets you are currently wearing, but are greyed out unless you have all 5 pieces.
If you have 5 pieces of a particular set you can select the appearance to that, which will render all other items on the character to look like that set.
Crafted sets would require all pieces to be the same style and if selected would extend that style to all pieces on the character.
Seems pretty simple to implement as the assets are all there. Would provide some function to the 'appearance' button later on in the game.