I am under the assumption that the Jubi is a manifestation of nature while the Rikudou Senninis a manifestation of humanity. I also think that Yin/Yang Release - there is more to it than it appears along with KKG and the Five Basic Transformations.
We know that Kurama stated that the Jubi has no ideals or consciousness.
Now, most think that the Jubi is evil. But how can something with no ideals, consciousness or mind be evil? Orochimaru could be considered evil because he experiments on people etc. but Jubi is like a rock. That rock if whipped at someone's head can kill somebody - does that make the rock evil? No it makes the thrower evil. Who is the 'thrower' in this case? Rikudou Sennin.
Now before I get into that, I will explain why I think that the Jubi is the manifestation of nature.
That is the basis of chakra and where did chakra come from again? That's right the Jubi. Fire, Water, Earth, Lightning, Wind are all aspects of nature. Now there is even more to this theory. Alright, I will dive into another universe for a second to show you why I think this.
That is right! Lion King
We should all, considering we are all 10 years old or more, have watched it and know about the Circle of Life.
Basically to sum it up if you didn't watch it, a lion eats an antelope. Antelope eats grass. When a lion died, his body 'becomes' the grass. So basically, Lion > Antelope > Grass > Lion. You may be strong against one thing but you're weak against another. What is something a lot like that? That's right, nature transformations. Keep in mind, they call it NATURE transformations.
Fire (火, Hi) natured chakra allows for Fire Release (火遁, Katon), which is strong against Wind but weak against Water.
Wind (風, Kaze) natured chakra allows for Wind Release (風遁, Fūton), which is strong against Lightning but weak against Fire.
Lightning (雷, Kaminari) natured chakra allows for Lightning Release (雷遁, Raiton), which is strong against Earth but weak against Wind.
Earth (土, Tsuchi) natured chakra allows for Earth Release (土遁, Doton), which is strong against Water but weak against Lightning.
Water (水, Mizu) natured chakra allows for Water Release (水遁, Suiton), which is strong against Fire but weak against Earth.
Now moving even deeper (don't, That's What She Said me -_-), Kekkai Genkai!
Notice how they're all linked. I think that every KKG has a weakness to another KKG or another Basic Transformation. It happens with the 5 Basic One; why not all?
Now why did I say earlier, or clue earlier that I think that the Rikudou Sennin is evil? It is because of the greed of humanity I say that. Every culture, religion, etc. says that greed is bad but a natural part of being human. Why did the Rikudou Sennin stop the Juubi? Simple, to make it easier for humans to live. Juubi is the reason why nature (plants, animals etc.) thrived and it kept in balance with the humans but Rikudou Sennin destroyed that balance. Hey what do you know, there is something in Japanese mythology which clues at balance.
Rikudou Sennin later discovered this mistake and he showed it through this panel.
Wait, wait, wait WAIT. Did the Rikudou Sennin say they will all become .. one? If they did, what is that? That is the Juubi - is he INSANE? No. The Sage knew that without nature and humans co-existing equally, peace can't and never will be attained.
Nature isn't a physical entity but a spirtual one; it exists in the mind and soul. Humanity is a physical entity. Yin Release = Spritual Energy , Yang Release = Physical Energy, therefore, Nature = Yin , Humans = Yang