Obito hasn't gone blind yet from using Kamui so many times because of the Senju DNA that makes up his entire right half of his bodyThis^ . . . . . . . OBVIOUSLY NOT
Why both eyes? He has got Mangekyou Sharingan so it means if he has to use the Kamui too much he gets blind. Not if he's got the Rinengan. He would still have an eye. And obviously Rinengan > Sharingan..
I wonder how Obito hasn't got blind yet. He always uses Kamui ..
OT: Sharingan & Rinnegan --- Susano'o great and all, but I would muh rather have complete control over the Statue of the Juubi. Susano'o grants the user excellent defense but at the cost of the user's chakra for every second it's active. Gedo Mazo is a powerhouse with near-infinite chakra potential.