I'm going to start this post off with a story:
The same summer that I got my driver's license, the most important bridge in my hometown needed to be rebuilt. It was the kind of construction project that had everyone talking. Literally a half million people would be required to drastically alter their daily routines. A friend of mine even quit his job in lieu of tripling his commute time. This major transport artery was so close to my father's business, we had even more serious concerns at home about how traffic would be affected. Anyone who knows much about public construction projects, especially in areas that get ice and snow, will tell you to double the time they are supposed to take for a conservative estimate. I was 16 when the project started, and my father half-jokingly told me we would be lucky to use the new bridge to take me off to college. We did use it to take me to college. And to visit the college my senior year. We were using that bridge six months after construction began. Six months ahead of schedule. When the announcement was made that the project was completed, everyone in the community was surprised. Except my father. He told me about how this project had a contract that was unique at the time. For every month that the project was late, the contractor had to take $1 million off of the price. And for every month that the project was done early, they got to charge an additional $1 mil. The government agreed to this deal in a heartbeat because no one thought the project was even possible in a year. I'm sure someone literally laughed out loud when they heard about the clause for finishing early. And yet, we all got our bridge back early, and under budget even with those bonuses. Your econ teacher was right: people respond to incentives in a market economy.
You probably already figured out what this has to do with World of Warcraft. I'm honestly surprised that we are in yet another huge content drought, and I shouldn't be at this point. But, our community has been told a number of times that expansions will be roughly annual. They have publicly lamented content deserts (we're beyond drought at this point). Even worse, the last two expansions were horribly front-loaded. We got more content than most could handle in the first 6 months, and then, not much. And then nothing. And here we are.
So it is time for Blizzard to put their money where their mouth has been for years. While I would like to propose WoW going free to play any time a year goes by between expansions, that isn't likely. What may be more feasible is any time a year goes by without new content of some kind, we all stop paying a subscription until the content goes live. It still probably won't happen, but I think it should. Keeping players playing during these content deserts is very much in Blizzard's interest. As it has gone, tons of players unsub during these times. Then a new xpac is released and some of them come back. But not all of them. I don't know how many of my friends have left promising to return and are never heard from again. At least not in WoW. They are still gaming, many in Battle Net. But they don't come back to WoW or it's subscription. And at this point it's hard to blame them. If there were no subscription, I bet at least half of them would still be showing up to raid, if not playing the entire game more.
At the very least, this kind of arrangement would compel Blizzard to space the content they do have for us more judiciously. WoD would still be rather thin, but imagine if MoP or Cata had been under this arrangement. We could have gotten new raid tiers, or new troll dungeons, spaced out evenly over the course of the expansions. We wouldn't have had year-long periods with nothing other than Dragon Soul or Siege.
Ok, that last paragraph is what my history professor would call "counterfactualism." That aside, if you are Mike Morheim and Hazzikostas tells you, "We could make some new dungeons for them or give up $45 million in revenue each month for a while, what would your decision be?