Before Juubi shows his last stage/form naruto will activate FIRST his BM PERFECT form
Kurama said to naruto that his BM form was not yet perfect...
And after 8-mins in BM form kurama reached his limit.. he needs to gather enough chakra/energy to help naruto fight the juubi, madara and obito...
IMO The next time we will see kurama he will give all the chakra he gathered to naruto to transform into bijuu mode(BM) in PERFECT form... Naruto in perfect BM will have a chance to defeat the (not perfect)juubi but the juubi will also unleashed his final/last stage/form... I think there will be a battle between naruto in perfect BM and juubi in perfect form/stage.. Naruto will be defeated and kurama's power will be absorb by the juubi...
This is only a prediction and I know I could also be wrong.... what do you think?