I dont know why EVERYONE is saying it came from the Sage of Six Paths. Why in the world would the Sage give an instructional guide of how to get the most OP power and he shunned "power" being the main reason to lead? He never agreed with this mindset and this is exactly why he made the Younger son the true successor. Why give the Elder son the blueprint to get back to "successor" status and he wanted this for the younger son? Did he give the info to both of them (Stone Tablet and Hashirama's Scrolls) ...? I still dont think so, it would give the Elder son a chance to gain more power and overtake the younger son, I cant see him doing this. Its contradictory.
Madara was the 1st Shinobi to awaken MS (according to him LOL). If the tablet existed before this time, it would be like foreign language to the entire clan b/c no one would be able to read past a sharigan level decipher. The only way I'd support this theory is if it was the ELDER SON who created the tablet, not the Sage. I honestly think that information about obtaining MS eyes and above never existed on the tablet until Madara put this info on the tablet himself as Clan leader after he unlocked the secrets of MS & EMS & Eventually Rinnegan. The 1st Son was born with Rinnegan-ish eyes so i doubt he ever had MS/EMS. Madara either created it or added this important information to it.
-gHost Senju, K.U.S.H. Sage
Part of the Uchiha tablet is only capable of being read by someone with the Rinnegan, which prior to Madara, we only know that the Rikudou Sennin (So6P) had, not sure if the elder brother/son (he had swirly eyes, nothing like the Rinnegan. I'm not sure why you think that they're comparable, especially since we know nothing about them aside from appearance.) gained it or not.
Here's a link regarding the elder/younger son's abilities, granted I'm afraid the quality is not good enough in this one to see the swirly and non-Rinnegan doujutsu eyes of the elder son (you'll have to trust me or go back further for another link, but it's kind of waste of time...): :shrug:
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Perhaps the swirly eyes of the elder son and the Byakuugan can't read the tablet, as Tobi doesn't reference those eyes as being capable of reading it (see link below.). This doesn't rule them out, but it doesn't rule them in as it does the Sharingan. Otherwise, we know it progressively unlocks more and more information as you evolve your Sharingan->MS->EMS->Rinnegan. Thus, it's logical that such secrets were written by a Rinnegan bearer to me, as how would someone without a Rinnegan write the language parts readable only to a Rinnegan bearer? This is backed up below by Tobi's statement that the Rikudou Sennin was the creator of the tablet.
I'm not saying that the elder son is automatically ruled out by this, since I don't know if he ever evolved the Rinnegan nor his doujutsu powers, but there's no evidence he did, and it's speculation as to how his swirly eyes worked on anyone's part, including me.
Finally, and most importantly, it's explicitly stated that it's the Rikudou Sennin's creation by Tobi, his credibility is fair criticism of this point, but why would he lie about this? Tobi states, "...upon it are the recorded secrets left to us by the Rikudou Sennin..." It was when Tobi announced himself at the Kage Summit and his plans regarding the Juubi along with it's history with the Rikudou Sennin. Here's the link:
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Thus, there are two main reasons to think it was the Rikudou Sennin's creation.
First, we have that parts of it were encoded to be read only be the Rinnegan, and we know of only one Rinnegan bearer before Madara, who was the Rikudou Sennin.
Second, we have Tobi's statement (always aware of his credibility issues, but what's the motivation?) that it was the Rikudou Sennin's creation.
Peace
