So far, from what I hear the official opening date is April 7th. There will be previews for Disney Vacations Club members in late January (I want to say the 26th to the 28th, but don't hold me to it). The chances of soft openings immediately after the DVC previews are rather good, as Expedition : Everest is a rather large E-Ticket that will have many kinks to work out before it's official opening. Mission Space is an extremely technically advanced ride, and opened for soft openings several months before. Anyone going to WDW anytime after January, make your way to Animal Kingdom, because you may have a chance to meet the Yeti (as always, soft openings are subject to change, and the attraction may open or close without warning, so if you're going, hope to be able to ride it, but expect not to be).
Yensid "I-wonder-if-the-Yeti-will-be-uncovered-during-these-previews" tlaw1969.