Me really, those are my reasons I thought it will be Obito :
- His name is was Tobi the same, similar to Obito.
- Kishi didn't created Obito in Kakashi Gaiden for nothing.
- We saw that he have only right eye, and Kakashi got his Sharingan in his left side.
- Kakashi used Jutsu similar to Tobi's when he chased Deidara.
- He was an Uchiha, who could it be? of course that wasn't Madara, Tobi's hair is similar to Obito's it's impossible for Kishi to change someone's like Madara his Hair.
- Madara don't have any reason to hide himself and use A mask we saw that Tobi has something to hide.
-Right side of his face was crushed - that confirmed it..
- He lost to Minato, so no way it's Madara, Madara would rape Minato.