Forgive me if I am remembering wrong, but didn't they announce one year as an "April Fool's" that Panderia was going to be the next expansion? Just goes to show how the game culture has changed. From joke they would never do to serious expansion.
The Pandaren were an April Fools joke the Blizzard put up on their site as a race for WC3, not WoW. They got so much positive feedback that they actually put them into the game in the expansion. Then they nearly introduced them as a Horde race in the Burning Crusade but they went with Blood Elves instead.
people have been asking for the Pandaren. If you look at forum threads surrounding the Pandaren Monk companion pet there are thousands of people wondering when Blizzard will introduce Pandas into WoW as a playable or NPC race. Now Blizzard puts them into the game as an anchor race for a new expansion, and a minority get pissed off because "Blizzard is trying to appeal to six year old Kung Fu Panda fans" or "Trying to win the Chinese market because they know WoW is dead". This expansion looks like it has so much content to offer, I think people who aren't at least curious enough to stick around to see how it plays out are going to miss out. If people want to quit, that's fine too, but if they think they are going to get a substantially superior and unique MMORPG experience out of SWTOR I think they're going to be in for a bit of a surprise.
I think raiding in 5.0 is going to be absolutely magnificent as far as the content execution goes. SWTOR and Bioware will definitely be playing catch up in that area for a long time.