I think the first few hours are going to be pure insanity, no matter what
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But I think after that, we'll see it spill out all over the place. West Karana is full of stuff for low level players to level up on for instance. On Blue there's no reason to enter the zone until you're ready for Scarecrows or Bandits, but there's plenty of lower level animals no one even bothers to kill, because they can just go to Qeynos Hills/Everfrost (closer), or Blackburrow (has fangs) instead.
But if all those zones are full ... West Karana will be far from the only zone I think we'll be surprised to see low level people XPing in.