How does ANet gague Living Story popularity?
Firstly, that's the wrong question. It should be how *can't* they gague it's popularity. Number of players playing the content.
There are a lot of achievement point hunters in the game, which Anet capitalised on with the use of Achievement Chests. These players will gravitate towards whichever content offers the most achievement points; they'll do all the dailies and monthly achievements and then move onto the motherload: the living story. Completing the meta rewards you from anywhere between 25-50 AP on it's own, not to mention all of the achievements in the panel. Just add them all up and you'll quickly realise why the living story is being driven by AP hunters. How many servers continued trying to kill the triple wurm head after completing their metas? How many achievement hunters started clogging up the WvW queues? Do you think they really like the format?
They're not only great for achievement point gain, however. This is where karma comes in, as every creature you kill becomes a zergy short repeatable chain that can net champ boxes and massive experience and karma gain. Karma which is seen in no regular content but WvW (which they will be pushing for esports esports esports esports on sooner or later). Think about all the karma gain from fractals (recently spotlighted and patched, superior karma gain to dungeons) and Tequatl (far superior karma gain to all other world events)
The final reason of course, is the unique rewards that are typically either account bound and require living story loot to obtain or items which will cost a hell of a lot of gold otherwise.
Now, the original question is for you to try and answer. I have met a lot of dissatisfied players over living story, so I can't call it a success, by any stretch and I can conclude that the majority of players are participating in this content for incentives put in place other than good gameplay or plot.
Edited by Minion, 20 February 2014 - 01:15 PM.