I think this can be an excellent feature for WoW. Well, if they only make the easy difference that you manually can change between phases you have been. Basically, you could change lots of things, like having Onyxia left in SW in one phase, but when you've done that quest (or other related quests, or are at a certain level) you will be in another phase. Through this system you could actually invade Theramore, burn it to the ground in one quest, while others are doing their regular quests there and are none the wiser.
It would be possible to have an ACTUAL story line with ACTUAL events, and people would still be able to go back and help friends!
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