What I find more interesting is how the infinite Tsukiyome was stopped. Did Hagaromo fight Kaguya? According to some theories, Kaguya became the Juubi itself.
The point of giving Naruto and Sasuke powerups would really be pointless if he would come out to join the battle. I would be grateful to see on how they defeated the Juubi though.
After the Naruto and Sasuke, and the Allaince battle against Madara, the Sage starts off the new Arc talking with his brother. Epic!!!!!!!!!!!!!!!!!!!!!!!!!
There's way too much backstory and other questions to be asked. WE will see him again and I think when we will see him again he's going to explain the importance and the origins of the Uzumaki clan and hopefully the Hyuga clan also. Hagoromo did reference his mother having the Byakugan.