Basically Google offers a service which gives you the history of how often a given keyword has been searched for. The interest in MMORPGs went up from 2004 to 2009, and declined since then by 45%. The peak of the hype for World of Warcraft was in 2005, but it still has more searches than Star Wars: The Old Republic. I am aware of these numbers because the reader numbers of my blog also declined. I'm still not doing badly compared with other MMORPG bloggers (and I'm still the top search result for "MMORPG blog" on both Google and Bling (US)), but the trend is definitively downwards since the peak in 2008. Measured in daily blog visitors instead of search engine searches, I went from 3,000 visitors a day down to 2,000. Even the interest in blood elf porn is down by half. :)
So, yes, I do think we have sufficient data to suggest that the general interest in the MMORPG genre is declining, in spite of the games still to come. While the reasons for that are open to discussion, I do believe that a certain stagnation is most probably to blame. I once discussed the "possibility space", that is how wide a range of different features and game mechanics a game could have while still being considered a MMORPG. And compared to that possibility space, the majority of existing MMORPGs of the last decade are all huddled together in one tiny corner. Whether you label that corner "EQ clones", "WoW clones", or "themepark MMORPGs" isn't important. But it is obvious that at the end of the decade the interest in minor variations of the same theme is in decline. And I don't think that adding light sabers to the same old formula will change that. I have no idea what game it would take (Guild Wars 2? Titan?) to revive that interest again. It is possible that MMORPGs are taking the same path into decline as let's say trading card games. People seem to be more interested in Facebook games these days, even if the interest in any particular game dies quickly.