I'm not entirely sure about what part of the Juubi's anatomy that was, but it seems to be unraveling, showing us that the Juubi has finally amassed the power to accomplish it's full potential. As to what the full potential is or what dangers it poses, we do not know. What we do know is that the part of the Juubi (which looks like a tail to me) seems to be spiraled. Once again, why, I do not know.
I think that the ten tails has or is part of wood style and were gonna se some awsome fights :D its like a plant on the 10 tails arm but the big Q is will it reach the ten tails whole body and save it from the "The Shinobi Allience jutsu" :D