Back when the 3DS was revealed, Ubisoft had plans for creating an Assassin's Creed game for the 3DS, this game would be called Assassin's Creed: Lost Legacy, but during the time from then to now, Lost Legacy was never finished.
It doesn't mean that Lost Legacy wasn't completely lost, Lost Legacy eventually made the foundation in which Assassin's Creed: Revelations is based on. Lost Legacy was turned into Revelations, but being released for consoles instead of the 3DS.
Darby McDevitt, Assassin's Creed: Revelation's head writer, said, "The story that was announced about Lost Legacy was that Ezio goes to Masyaf and investigates the holy land." In Revelations, that's what Ezio does, he heads to Masyaf at the beginning of the game.
Even though Assassin's Creed: Lost Legacy is dead, it eventually helped morph Assassin's Creed: Revelations into what it is.
