For those of you who are out of the loop, phasing is the new technology that World of Warcraft (and Lord of the Rings Online, to some extent) makes use of to change the world as the player completes quests and progresses in the storyline. For example, doing quests to retake a piece of the world map from the monsters might actually lead to a new base camp being set up by NPCs instead of just completing the quests and having no change occur in the world.
But phasing has its own problems, as Marc has shown. Sometimes you may enter a phased state only to find that the event contained within it was started by another player, or you may find your epic storyline moment ruined by an inconsiderate person.
So, with all of this in mind regarding phasing, here's the question: "Is phasing the new instancing?" Certainly it won't replace instancing completely, but should we put phasing into the category of "great leaps in game design" or should we stick it somewhere in "fads that will die in 2 years?"
