Idea: To have a regular new item (warrior) introduced that is based on a player in the game. The chosen player would earn this right by winning a 'trophy'. That trophy could be anything but suggestions include; highest bounty earned, most kills, most bosses helped etc ...indeed the data is all there in the World leaderboard. Advantage: Players would want the honour of having a warrior created based on their hard work. It would encourage gameplay and competition. Ease of implementation: Easy based on the basic version above. IN terms of design, I would suggest a 1 month time between the 'trophy' being awarded and the warrior being introduced as a limited item. This would allow collaboration on design with the player themselves. Additional features could be to do something like most kills in a given period (which may rely on a program being written to compare a snapshot of data with another). Also, to encourage lower level players you could have something like "most levels gained in x days".
I love this idea! I notice that there is an item called "Bob's Voyager" which I think is based on one of the long playing Viking's who recently died. So the idea already has been 'approved'! But i think the idea of extending to deserving players is a great one and gets my vote.