Kabuto said He wanted a Young living Uchiha, Maybe Sasuke is the last living Uchiha. The person calling Himself Madara may not be an Uchiha, but someone like Kakashi who has come to own a Sharingan. That would explain why a mask with one eye opening instead of two eye opening. The Real Madara had two eyes if he wanted to hied His face He used a Mask with two eye opening. Why cut your power in haft with one eye when you can use two eyes?