Blizzard are bringing back the Joyous Journeys buff, with an extra 50% experience for players!
XP Buff (Source)
The roads in Northrend are icy and fraught with danger. To help you continue your journey, players will get the benefit of the Joyous Journeys experience buff*, which will increase experience gains by 50% for all players through level 80! It’s a great time to finish leveling a character, create a new one, or invite friends to join you in your adventures.
Players can also visit any innkeeper in the capital cities and Dalaran to turn the experience buff off or on. The Joyous Journey’s experience buff will be available during the Ice Crown Citadel content update and until further notice.
*Experience buff not available in modern World of Warcraft® or World of Warcraft® Classic Era.