The main reason this will not kill WoW is the same problem that affected every other mmo claimed to be the WoW killer; they haven't done anything significantly different enough to make it so. Sure, they've limited the number of abilities on the hotbar and made them each more powerful, like a moba game, and added a stamina bar to use for different actions, but it's still just a hotkey mmo. New lore won't be enough to take away the majority of the WoW fanbase.
A less important reason is that WoW is already dead. Effectively the only people still playing are those that joined years ago, those people that have invested so much time into the game it is simply too hard for them to leave.
Exactly.
What COULD kill WoW is a real-time combat system or something DIFFERENT from WoW.
If you were halfway through Skyrim, would you stop playing just to play Skyrim with different graphics and lore, and minor adjustments?
No. Would you stop playing Skyrim if you could play a world that is larger, with a better combat system, graphics, and different features to make it interesting?
Much higher chance.