Here's an unpleasant truth: To want, motivates efforts to gain. To have, inspires no action.
I see an ominous parallel between Cataclysm and Heavensward. WoW Cata is generally regarded as the first moment WoW slipped up badly enough to precipitate a mass exodus - everybody knows that bit, already. Have you asked yourself why?
Plenty of players will tell you "oh, yeah, I quit at Cata, it sucked", but they'll seldom have concrete reasons behind it. They know it sucked, but lack the words to describe how the game ceased to be compelling for them. This isn't because they don't know a good game from a bad one - it's because Cataclysm did right when it should have done wrong.
Cataclysm streamlined the raid environments to an extreme degree, and ensured that absolutely everyone could experience everything the game had to offer without great investment in one's character or the server's raiding community. It gave players everything it had on a silver platter, and they didn't need to work for what they got. This was met with satisfaction, on the surface. It seemed good, at first.
And then, having been carried up the mountain, the player base found itself with nothing to motivate them to climb. Higher numbers is a meaningless and shallow motivator - real excitement from getting a piece of equipment comes from knowing that it can help you on your journey to see and do greater things. So, having seen all there is to see, players quit en masse, confused and disenfranchised by the hollowness of their journey.
Cataclysm gave players what they thought they wanted, and that was how it dealt the first mortal wound to WoW.
Now, let's talk about Heavensward - having outlined the above, I can keep this part of my post brief. Heavensward has undergone an uncannily similar metamorphosis - developers, concerned that the majority of the player base hasn't scaled the mountains that were set before them, gave the players the opportunity to have a ride up.
Look at this story, and look at the forums. Now look back at the story, and again, back at the forums. Look at the confusion on the forums. Look at the disagreement. Why is it there, now that this game caters to all play-styles? Ask yourself, does this look like a group of people who know what they want, collectively?
Does this look right to you? I never cleared 40-man Naxx, and that fact never pushed me from vanilla WoW. It was always hanging overhead: the promise of further adventure.