you ca see the sage of the six paths correlation already. thats obviously why that part of the story was inserted. gaara isnt confirmed dead, of course naruto can still make it to him gain his chakra (which is still influenced by the 1 tails) and either madara, sasuke or obito will have the other form of the sage of the six paths ..or something to that nature.
The nine bijuu's are inside of some sealing spell/barrier.
And even son goku said that "be sure to teach him"
So, Son goku felt that naruto is the one that the sage was talking about, so maybe what he mean about "be sure to teach him" is to let naruto know their names for the time comes that their going to be whole again inside of naruto
Maybe summoning the juubi isn't that easy. it needs some info/knowledge. And it's the fail-safe method of the sage. The only one who can control the juubi is the friend of the nine bijuu's.
NAruto : *creating some hand signs.* Then "rikudou sage full-transformation-bijuu's-seal" Then naruto will going to call all the names of the bijuus.
Shukaku, matatabi,, isobu, son goku, kokuou, saiken, chou mei, gyuuki, kurama. Come now, juubi.