But Azshara does get my vote, because it can actually have a little bit of everything in it.
We've got the Tomb of Sargeras, home of many demonic relics, which can be the basis for a Legion plot. There's some kind of advance force seeking to use the Tomb to summon the full armies of the Legion onto Azeroth.
Then there's N'Zoth, and the Emerald Dream, which would likely show up in a Isle of Thunder/Firelands-type role in the expansion. As well as potentially having Ny'alotha appear as a zone.
And of course, we have the big baddie Azshara. Who's status as most powerful mage ever likely has only grown since she kidnapped the Elemental Lord of Water, Neptulon.
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"I quit WoW."
If I say it's Azshara next enough times, eventually I'll be right. So here we go again. It's got to be Azshara next, so get ready for the Sylvanas expansion we inevitably get instead!
They need to put giant robots in as part of a mini-game like battle pets, everyone gets their own giant robot that can be upgraded and leveled then used in giant robot pvp and fighting against giant sea monsters. The only downside is that we would need an explanation as to why you wouldn't lead with summoning your giant robot in almost every fight situation.
Blessed is the day. And the one Who destroys the day.
Blessed is this ring of fire In which we live
Blessed are those who stand still In their confusion.
Blessed is the field as it burns.
Most people would rather die than think, and most people do. -Bertrand Russell