Hi all!
I think exclusiveness comes hand in hand with the fantasy of the class. Druids are seen as a very versatile class capable of performing multiple roles within a party. A class which can act as a healer, melee dps, caster dps and/or tank is exclusive on its own merit. However, if I had to think about something exclusive for druids it would be, without question, the ability to shapeshift and use different avatars depending on the role they are carrying out. I also believe that it would be awesome to have class inspired armor sets on a cosmetic level, a mount of its own and quest chains related to the class fantasy. In fact, it would be awesome if each class could have an arc of quests related to its own fantasy. That would reinforce the fantasy of the class, the game and the world and it would create a feeling of attachment to the class you are playing.