Usually, the event has appeared in the first week of May, so lots of players were wondering what exactly had happened to it-- were the children going to be abandoned this year? But though Blizzard hasn't given an official reason for the holdup, most likely it was because they're adding new Outland versions of the event, including all new pets (I'll be running to get my Metroid pet ASAP).
And finally, while Blizzard has not officially announced a date yet (do they do anything officially anymore?), the patch has been showing up on the background downloader, so it's a pretty good bet that 2.1 will be hitting tomorrow. By this time next week, you too could be carting little Dumbo the Elekk around Outlands.