just saying and I know you could control it with sharingan and rinnegan
just a thought
I actually agree with your theory. What else is Madara trying to gain from his fight with Hashirama?
There seem to be 3 aspects of the sage's power already, one being sage mode, displayed by Kabuto. Obito is displaying the jinchuriki aspect of the sage's power. Obviously Madara represents the sage's eyes, Kabuto the body, and Obito the jinchuriki.
I think if Madara could use sage mode, he would be 2/3's of the sage of 6 paths abilities, Obito would still be 1/3. Madara would probably try to complete himself at that point and go for the 10 tails.
Unless Obito and Madara aren't actually trying to become the sage of 6 paths (like Kabuto was). If they plan on settling for an infinite tsukuyomi when their power is incomplete that would be foolish.