It does have some similarities to wyverns, like a pair of eagle like feet 2 wings, tail with what seems to look like a hand (even the wings look like hands at the end of each), but I think even the more unknown theory by kotaku might be right, but I think this will be the first time they would use biology as inspiration, because normally they use myths nature and a bit if common sense in shaping legendaries, but I just cant unsee how yveltal is based of a wyvern, if you imagine that wyvern in that pic there flying it looks like a "Y", and then there's the axis theory that comes to mind which gives way to xearnus as a second legendary, I don't know maybe they actually went all out and mashed up everything they could into these legendaries, maybe?