sage mode + rinnegan=New eyes
I don't want to but details but.
kyuubi looks like he has a type perm.sage mode the black space from his ears to his eyes looks like kabuto dsm.
But I wonder if if you mix sage mode and rinnegan powers together can you form new eyes/power.
juubi=An unstable power full of natural or nature (i forgot) energy or could be an unstable sage mode madara has and controlled sage mode on him so say if madara puts his eye in then sum crazy **** start happening it could be by madaras will or it could be something that will happen randomly.
these new set of eyes can be used while the juubis within you mabe naruto would get his own juubi and mix his sage mode with it and create a new eye.
I mean you know how naruto eyes change in bjiuu mode madara and obitos eyes should had changed also but it didn't it could mean 3 things
no sage mode (And)
both eyes don't match
real eyes have to be its owners
so if I'm right madaras plan to get new eyes could be this and his plan from he start is still on.