Blizzard Splash Teaser Unveiled

If you visit Blizzard's website you will be greeted by a beautiful splash screen featuring some kind of magic unfolding from the darkest, deepest corners of the Earth, together with what looks like a series of faint runes. As alawys, this is one of the famous Blizzard teasers for an upcoming announcement regarding, usually, a previously unannounced project. What could it be? :)