I had a revelation this morning as I was dozing in that half state between waking and sleeping. MMORPGs are the "point and click" adventure games of our era. Just like adventure games in the 1980s and 1990s they have enjoyed an explosive growth in popularity. Also just like point and click adventure games they have a fundamental flaw in that the games themselves are really quite boring.
I did a business course a few years back and one of the enduring lessons that stuck with me was that many market leading products force their customers to make compromises in order to suit the manufacturer. Once alternatives become available which do not force customers to make those compromises the market leader is doomed. MMORPGS force their customers to endure hundred of hours of boring repetitive game play so that publishers can extract the maximum number of ongoing subscriptions from a limited amount of content. This is an unsustainable business model once alternatives become available which offer similar gaming benefits without the tedium.
Therefore on the basis of no research whatsoever I am going to go with my hunch and pronounce that the MMORPGs are passing fad that will vanish quite rapidly some day in the near future when players wake up and realise that there are many more enjoyable ways to invest their gaming hours.