As you can tell from the title, the release date for the next World of Warcraft expansion Legion has been announced. It is scheduled for the 30th August, which is about 4 and a half months away.
Official Blizzard press release – http://blizzard.gamespress.com/THE-LEGION-INVADES-WORLD-OF-WARCRAFT-AUGUST-30
By pre-purchasing the expansion you get 1 boost to level 100. Pre-purchasing Legion will also grant early access to the Demon Hunter prior to the expansion’s release. During the pre-launch early-access period, players will be able to complete the Demon Hunter’s unique starting experience on the shattered, Legion-corrupted world of Mardum and achieve level 100, leaving them fully prepared to join their allies on the Broken Isles the moment the expansion launches.
Stay tuned for more content – coming soon (TM).