I just look at some of these upper-tier players, and I can't help but think "they can't be having any fun"
Compulsive gamblers who are in every real sense of the word addicted to the act of gambling will often curse and swear and grief themselves over the chore of wasting their time and money. It is 'fun' to them, but not in a way which someone who is not within the same pathological mindset would consider 'fun' upon observation.
It is the same thing for most hardXcore players in WoW. It is 'fun' to them. They will play until they collapse from exhaustion and ***** about the entire experience. It's still the experience they most pathologically crave.
The odds that something will surpass WoW by virtue of being 'better' is not likely at this point since the Blizzard offices are appropriately researching and applying the nature of our brains and our compulsions in a
scientific manner to the gameplay. It was the result of their psychological research that resulted in their newly mathematically calculated drop rates and progression times and even the 'shininess' of equippable items. A game that does not run this sort of skinner-box experiement on its players so exactingly measured to maintain the button-pecking treat-dropping environment that so readily addicts people? It will lose out to WoW because WoW is the better drug.
Nothing can be as popular as WoW, really, without aping this. Any new franchise that approaches WoW's popularity will do pretty much the same things with our heads, just with different visuals and canon.