Looks like the cat is out of the proverbial bag that Aion 4.0 is launching in June (obtained from the NA forums). It'll be called the "Dark Betrayal" expansion and will be the equivalent of Korean Aion patch 4.2. This particular patch has both the Bard and Gunslinger classes in it.
Additionally, in order to celebrate the first anniversary of Aion going free to play, there will be events from April 10th through 17th. There will be a Decorate the Cake event (where you collect aether flames to trade for candles for the cake). There will be special offers from the Black Cloud Marketplace, including some supposedly free items.