I know there is confusion, as to what Sasuke's possibilities are, so I'm attempting a guess on past situations...
"Madara Uchiha was the first Uchiha to awaken the Mangekyō Sharingan. He eventually grew blind from overusing it, and only by taking his younger brother, Izuna's, eyes did he regain his sight. This also gave him an "eternal" Mangekyō Sharingan that gave him great power. His Eternal Mangekyō Sharingan looks like a combination of both his first Mangekyō and Izuna's Mangekyō
Now if we replace Madara with Sasuke, Sasuke's should look like a combination of both his and Itachi's. But I question some things, why would they just LOOK like the combination, and the wielder of the new 'magic eyeballs' not have the abilities of the added brother as well. Something to think about...
Additionally at the bolded, I'VE NEVER SEEN THOSE EYES (COMBO) IN THIS MADARA EXCEPT IN ONE FLASHBACK. But could that possibly mean that in a battle of the magnitude of Harashirma vs. Madara, that in losing 1/2 of the doujutsu component of EMS was sacrificed for life, but the powers of MS like Amaretsu, & Susanno are not available anymore. Until maybe another sacrifice of another EMS replaces said component.
I'm starting to feel like Jesse Ventura, enough, what say you?