In an interview with the Chinese gaming site QQ during Chinajoy, World of Warcraft Lead System Designer Greg "Ghostcrawler" Street let drop that a new class is being considered, one that is focused on buffs.
This has been speculated about for a long time, and previous comments by Blizzard designers have indicated they believe there's room for another class. However, this is the first time we've heard what they're considering implementing. A buff class would, well, give out buffs to other players increasing their abilities. We don't know anything more beyond that, however Blizzard has had buffs as a major component of classes before in the early (Pre-Burning Crusade) designs of Paladins and Warlocks.
Please keep in mind that this is an interview conducted in another language, and while we've acquired a human translation of this particular part of the interview, it is possible things have been lost in translation.
Many thanks to Spoiledleftie on Twitter for assisting with the translation.