Make Achievement Skins Accountbound
All skins should be account bound plus they should be kept in a closet/wardrobe/library/dressing room. That way if I want to use a shield skin for my Warrior instead of my Guardian or use it on both characters it would be possible to do so without having to buy/craft another piece of armor in order to transfer the skin or have to go out and get 2 identical skins. Even a tab under the “Collections” section in the vault where once a skin has been achieved/purchased/found it can be used on any character meeting the base requirements.
Even the store items such as sunglasses or the devil horns in time slowly start to clutter up the vault. I have one complete bank tab filled with various skins that are not yet assigned to characters plus skins that were assigned that no longer suited that particular character but are now locked to a piece of equipment until I decide who to transfer it to. At this stage of the game when I have 8 level 80s in exotic transferring skins can become problematic if you take into account the type of armor/weapon and the runes/sigils in that item.