I've been kicking this idea around for a while, but what about whole new "untamed" zones? Expanses of the areas we already have that are blocked off by NPCs who grant access based on level or quest prerequisite. The zone is about the size of current areas but is swarming with boss, strength monsters. There could be unspoiled nodes and treasure coffers that spawn tied to a certain mob's death. They could offer daily quests, like an "Expeditionary Mission" that require retrieval of items that have to be harvested. This could tie into another idea I had about using certain DoH classes to repair/clear obstacles, like an escort mission (minus the dumb NPCs). Enemy spawn rates could correlate to the number of people in the zone (to a degree).