Yes, Madara and Izuna read the tablet with their sharingans at first, learned about the mangekyo sharingan and gained that. Then they could read more and probably learned about the rinnegan then.
Now, Sasuke only read the tablet using his sharingan. As far as I know, he never came back to Konoha after he got his mangekyo. So he hasn't read the tablet for years now. The only way he could learn of the rinnegan without the tablet would have been from Tobi or Orochimaru. But I doubt Orochimaru talked about it, cause Sasuke would have easily been interested in it.
I think "that jutsu" is just the tailed beast bomb which Naruto just mastered. Either way, im more interested in knowing what Kabutos "that jutsu" is. Considering the insanely enormou power at his disposal, to think that he still has a back up jutsu is incredible.
Originally Posted by Rlinfamous