Just checked. Here's what Kishimoto really said.
"Kishimoto-sensei addressed curiosity on whether Madara can be defeated. He responded that while he did make him really strong, Madara has to be defeated somehow otherwise the story won’t be able to progress. He continued by saying that he has to figure out how to defeat Madara and that he’ll have to think it over with his editor."
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^The last chapter that came out December 2013 was when Madara stole the Kyuubi from Naruto. So after making this statement Kishimoto proceeds to make Madara become the Juubi Jin, absorb the God Tree - thus gaining immortality, regain his second Rinnegan, then awaken the Rinne-Sharingan (third eye), cast the Infinite Tsukuyomi on the world, tell Naruto and Sasuke that he will fight seriously and the final battle has begun now, then Black Zetsu back stabs him and revives Kaguya. All this happened by May 2014.
Based on this he didn't originally plan on having BZ backstab Madara knowing that was his weakness, but he was smart to make use of this established plot point considering that doing so wouldn't be an asspull.
1) Orochimaru stated that he was able to hear everything that was going on from within Kabuto and even gained Kabuto's memories when he took his power back. Based on this it's clear that not only did he know that Madara had Wood style, but also the Rinnegan. 2) Do you really think Sasuke never surpassed even EMS Madara? Or that EMS Sasuke wouldn't ever surpass EMS Madara? He had his EMS for a few hours during the war.....3) You're right about Sasuke receiving Hashirama's chakra. I never read the Viz nor even seen anyone mention it before. They always say Hashirama gave him a jutsu. 4) "A SHARINGAN like mine....didn't Madara also address this earlier when he pointed out his Choku Tomoe?
*stronger
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