Everything Yin & Yang
As we discover Imagination and spiritual energy is the basis of yin power. Able to create shape and form from nothing. Vitality (Life energy) and Physical energy is the basis of yang power. Able to breath life into form.
As we know the the Rikudou sennin split his yin power into his oldest son and his yang power into his youngest son. Uchiha and Senju. The Senju clan was split into the Uzumaki clan. They were known for their great life energy.
Tobi has Hashirama's cells but if the clans were split, Hashirama wouldn't have the Rikudou's great vitality. In a sense Tobi isn't complete until he gains a Uzumaki cells. Izanagi is the combination of the the Rikudou's yin and yang but the Uzumaki's have the life energy.
Vitality which I would assume would be chakra, because chakra is life energy. As we now Nagato was a Uzumaki, his chakra reserves were spectacular, Kushina after birth got the the kyuubi removed, still lived, faced the kyuubi and had enough chakra face the kyuubi in Naruto's mind. Testaments of the Uzumaki's life force.
The only true Senju we know is Tsunade. Her grandmother is a Uzumaki and grandfather was a Senju. That's exactly why Tsunade has great physical strength and she is the best medical ninja in the world.
Medical ninjutsu would assume to be yang power. by adding life energy into someone's injury. Shikumaru's shadows could consist of yin power by add yin power his shadows would create and take form.
As we see Naruto has the kyuubi's chakra which is nothing but life energy and sage mode which is nothing but an increase in physical energy. Maybe that's why Naruto is perfect in learning sage mode it's like the missing link to his senju physical energy and the Rikudou cloak is probably reacting with his Uzumaki blood turning the chakra into vitality.
As we see yin power can put shape and form from nothing. That's why Sasuke's EMS can bring out the powers of gods.
If Naruto and Sasuke were to combine powers, Naruto's Rikudou sage mode could actually breath life into Sasuke's Susano. Naruto and Sasuke are the imperfect version of the rikudou sennin.