I mean, seriously.

A. It's Madara's brother.
B. It's Obito.
C. Danzo is just pulling some Dr. Frankenstein (nickname from gabzillaz).

The only debate I have with the first two theories is the side the sharingan is on. I lean more towards the third theory. Danzo's other eye normally looks different, so it may look like he had a sharingan transplanted. Maybe Madara gave one eye for him in order to aid in a plot? He has just one hole for one eye with his mask. Perhaps Danzo simply took a remaining eye and pulled a Kakashi? Who's to say?

Must I also add on the bandwagon how cool the Cloud-nin are?

Also, Naruto's mug shot when Sai stood in front of him against Karui. Is it bad that I laughed at his facial expression? :/
Perhaps I was in a goofy mood.