The fight itself is intentionally easy; any tank and healer combination can probably duo the boss if necessary, but you won't have to. So far, I've had suitable "groups" form in under 10 minutes every day, morning or night, that I've attempted the event. I use quotes because you don't actually need to be grouped - all players in the area during the fight, or who show up for a minute or two after, can get credit, even if they are not grouped with the player(s) who killed the mob. It's even a rare occasion for cross-faction cooperation - the healer needs to be the same faction as the tank because you can't heal hostile players, but DPS from both sides are free to pitch in.
Towards Pandaria
Given that the event only drops cosmetic items - other holiday bosses also have loot - its popularity is probably a minor success. I'm even working on Archeology, since I'm flying by zones that have relics in them anyway. That said, it's possible that Blizzard is using this as a trial run for promised open world content in Pandaria.
If so, the real question is whether players are willing to accept being forced to go back out into a world that so many have been so quick to abandon since the Dungeon Finder arrived. Blizzard's lack of success with selling players on the concept of challenging 5-man dungeons in Cataclysm, after the easy zergs of Wrath, may bode poorly for the popularity of extending this trend from optional holidays to WoW's core gameplay.