Since they added archeology to the game people are constantly learning new things about Azeroth's past and learning forgotten secrets. What if a raid were to come out in the future, much like AQ was, and it required the servers efforts to try to "piece together the mystery" of this new raid. One day you might need to contribute tons of NE artifacts, the next maybe troll ones. The thought kinda just came to me so the details arent exactly all their but it doesnt need to be some super elaborate event.