Took the words out of my keyboard. XD
Juubi-Jin Kisame floods the Narutoverse....
Imagine Hidan becoming the Juubi's Jinchuuriki. If one part of his body is cut off, the Juubi's regenerative power is going to recover it. He can speed blitz a lot of people and take their blood. Though, I'm not sure whether Hidan can become one because a living body is required and Hidan's body is no ordinary living body - it is immortal.
Gai body is too weak to contain the Juubi so it's impossible. Why do you think he stuck to mastering taijutsu? BTW 8th gate is a one time thing so don't get it twisted.This is one I left out, Guy would solo all of NV at that point, he might even not die because of juubi's healing.