Mythic just released Grab Bag no. 21, which is full of Hunty goodness. Players will be granted special access to a new dungeon called Hunter's Vale for one week. This dungeon is accessed from RvR areas and is not warded, which puts the tier 4 version on par with Bastion Stair. Each tier will get its own version and lower level players will even be bolstered once inside so they can contribute.
A lot of effort goes into the game's monthly Live Events and they seem to be quite a hit with players. Some of the events will be annual, like the Wild Hunt and Night of Murder and some of them will be unique and introduce game-changing content to the world (e.g., Rise of the Tomb Kings and Bitter Rivals). It doesn't appear as though Mythic will be letting up any time soon.