Seeing how The SO6P spoke to the beasts makes me believe they were never part of on thing and that the sage actually foretold that they would one day be a whole.
Either combined by power ( Uchiha, Gedo) or by love ( Senju, Naruto-Much)
Each of the eyes, becoming one of the nine tommoes visible in this beast's Rinnegan
Then ten-tail only be the results of such events that are yet to happen, it's powers would be at the use of the side that does use awaken it.
The sage said that they would be led down the right path, maybe because he was ultimately unable to decide and believed that it should be decide who was right between his son by history, the winner gaining control over power great enough to change the world through his own means ( Infinite Tsukuyomi or Love and peace)
This could also technically be linked with the prophecy on Naruto, if he fails to save the Bijus, it will allow the Ten-tail to appear at the command of evil and thus bringing destruction to the world, or if he succeeds, he could earn the powers to eradicate evil from this world ( Tobi, Madara ect) thus saving the world.
Yes this is one of the most far fetched crap I've ever thought of in my Life :|
