Now Blizzard risks a Crisis on Infinite Earths.
From an interview:
It’s actually not instances. What we do is we have different world states, and depending on what quests you’ve completed, it changes what world state you’re seeing.
what we call the phasing technology. There’s quests that you do when you arrive at a town that’s overrun by Scourge, it’s like a “Choplifter” quest, you have to fly in and rescue villagers. As you bring them back to your quest hub, those villagers are there permanently for you, whereas if somebody who hasn’t done the quest shows up, they don’t see them.
There goes the last pretense of creating a world.
That kind of feature is extremely easy to implement. If it didn’t exist till now it was simply due to scruples. Wasn’t there any other better way?