I was searching info on the bijuu's and came across this thread about them. Its pretty interesting and informative, so here's the link
none of it is my work, anyways what do u think of the thread
The part which explains the 8 tails says something interesting.
Yamata no Orochi awaits a genius of the Yagami (NOT the Kanji of Yagami from Death Note, but Yagami as in Eight Gods: 八神) clan, which is the arch enemy of the Kusanagi clan. The purpose is to awake it [Yamata no Orochi], in order to fight Kyuubi again.
we know kishi bases some of his work on japanese mythology, could this explain the mystery of the 8 tailed. In japanese mythology the god susasano killed the 8 tailed. We havent heard anything about the 8 tailed in the manga9
(we dont know its location or even if its alive) If the thread offers some truth, then it could explain why maadara needs sasuke. The thread says that a genius shinobi would revive or awake the 8 tailed. The genius shinobi could be sasuke, its explain why maadara wanted him and why itachi wanted sasuke to stay awy from maadara.