It's sort of like how Ubisoft keeps insisted that Beyond and Good & Evil's sequel is still being made ... yeah, sure it is ... in their developers' spare time ... which is like a few hours every week. Won't be surprised when that (and this one) get quietly canned.
Actually Ancel himself spoke about BG&E2 recently.
Another factor that is stretching out development time: "On this game, we're keeping the team small," he said, "to preserve creativity and so the game doesn't become a commercial product, so that it has soul." This also has the added benefit of keeping the budget low, limiting the chance that Ubisoft will cancel it.