According to the in-game calendar on the PTR, Noblegarden begins Sunday April 12th and ends Saturday April 18th! This is very awesome because it means we don't need to grind all the Noblegarden quests on just one day. There are also a bunch of new achievements for Noblegarden and the Argent Tournament, amusingly one for getting a Dual Talent Specialization. The most expensive 10 achievement points I've got so far.
Noblegarden is still not part of the It's Been a Long Strange Journey meta achievement, but according to this post, it will be added. Let's hope the 3.1 patch is on live before April 12th then.