The Pandaria Beta has apparently begun, kicking off what may be an unprecedented event in MMO history. We've seen seven digit applicant/tester numbers for beta tests of several not-yet-released games, but this is an expansion pack to a game that is - theoretically - running a live subscription service. When all is said and done, one million players - at least 10% and probably more of the Western subscriber base - will be eligible for invitations.
I'm pretty sure that no MMO has ever fragmented its playerbase in quite that way before, especially if Pandaria does remain in beta for multiple months (which Blizzard games, unlike many competitors, have the luxury of doing). In just under two months, these same players, along with non-annual pass customers who are so-inclined, will go tromping off to Diablo III.
Meanwhile, Blizzard has published multiple "post-mortem" articles about the currently live expansion - the technical term would be vivi-section if the patient were not yet deceased, which one would ordinarily infer from the continued live subscription fee. It's going to be very interesting to see how events unfold in Azeroth as this beta proceeds.
(Aside: Blizzard apparently decided to axe the notoriously-leak-prone friends and family Alpha - realistically, I doubt they were gaining significant testing insight from the exercise, while putting legitimate fansites in an awkward position regarding breaches of the testing NDA. I'd speculated that they'd do this two years ago for Cataclysm due to the rise of keyloggers.)