Blizzard is all set to drop its new expansion for World of Warcraft --Warlords of Draenor this year. Late in 2013, they dropped a surprise promotion for the add-on, noting that if you pre-order the game, you can choose one character to boost to level 90 when the game arrives -- which means that you'll be able to start the expansion immediately.
As of now it appears as if if you pre-order the game (which will be available soon according to Blizzard), you'll boost to 90 right away. If you go for the Digital Deluxe or Collector's Edition, you'll also nab your new pet and mount at the same time. They're also toying with the idea of creating a character boost directly (read: buy one) due to "fan demand", so we'll see what happens there.
Warlords of Draenor - Scouting Report [Blizzard]