Madara said there still next "transformation" for Juubi
this comes to my mind
1st form resembles shukaku/ one tail:
1st form Juubi
2 form resembles five tails
Jubi 2nd form
so 9 Transformation of Juubi will be something similar to them
so maybe it still has 7 forms resembleng all bijuus and last 1 will be Juubi that was shown with S06P?