Chris Metzen (SVP of Creative Development) just revealed live at the Mists of Pandaria Launch Party in Irvine they are currently developing a Warcraft encyclopedia akin of what they did with Diablo III: Book of Cain (by Insight Editions). This book was among the top Amazon best seller graphic novels.
He also revealed they have plans for Turalyon and Alleria in the next expansion after Mists of Pandaria. Sargeras plans somewhen in the future. Warcraft IV not in the foreseeable future, but Mists of Pandaria has sort of a spiritual feel — probably some of the plots might carry on in Warcraft IV?