As we suspected might happen when we learned that Noblegarden was removed from the in-game calendar, the Easter-themed holiday has been delayed. CMs are quick to note that it will be implemented "at a future date," but it won't be going live on April 12 as usual. We were warned that this might happen, so it isn't a huge surprise.
The likely reason for the delay is that patch 3.1 won't be ready in time, or at least that Blizzard isn't sure it will be - it would have to ship next Tuesday, April 7, to make it. 3.1 is a massive patch and I'm sure they don't want to rush it. Nethaera did mention in a reply that they are "still doing a little bug dance and squishing a few more before we decide [the patch is] ready to have its coming out party," which may imply that all that's left before the patch is ready is debugging. On the other hand, debugging can take a very long time, so we can't conclude too much from that.
Whenever it does come out (probably sometime this month), we will be enjoying a new, expanded Noblegarden. It's going for one week (previously, it was just a single day), and there will be additional content for us to experience, as well as presumably a title (since it'll be part of What a Long, Strange Trip, everyone's favorite holiday meta-achievement).