Masked 'Madara' is actually Obito who seems to have survived
Spoiler :
He was actually my primary suspect when I was discussing the manga with my brother since we figured his identity would probably be a character we know rather than a new one. And we didn't exactly know a lot of characters that were Uchiha. It just wasn't really confirmed until chapter 598 when Kakashi mentioned the Sharingan sharing the same dimensional space that we knew for sure it was him.
Now I'm just waiting on the manga to explain how the hell he survived those boulders. And why he didn't go back to Konoha afterwards.