Just announced at SOE Live. October 8th 2013 release; when it is released, VoA will become part of the Free To Play/Silver content.
Will have mercenary AAs and mercenary gear (4 slots), as well as the usual set of AAs and extra content, based around Lendinaria (a dragon), and entered via West Karana. Extra shared bank slots. Not much else is known at this point - but no level increase.
The pre-order bonus for Collector's edition is a mercenary chest item; also included are the usual assortment of a mount, mercenary skins and housing items.