If he had EMS he could use Perfect Susanoo
He could make clones and have them use the Perfect Susanoo each one possesing the Totsuka Blade and the Yata Mirror...and with Itachi's sharp thinking he could easily defeat anybody
Apparently only Indra transmigrants or those with Rikudou's chakra gain Perfect Susanoo.
His chakra wouldn't increase to the point where he could actually do that.
Why would Totsuka and Yata gain duplicates?
He's sick because of the side effects of MS so wont EMS cure it?
Yes it should.
However, that will only stop him from dying before a fight's over.
Itachi was said to have an incurable disease, same as Shin and Kimimaro.
It wasn't from MS, and EMS isn't going to cure it.
It actually was from MS.
Susanoo is stated to slowly kill the user, or more specifically it eats away at their life-force.
Sasuke also mentioned how every cell in his body felt like it was on fire while using Susanoo, establishing that it attacks the user's body... like a disease.
Sasuke, like Itachi, also coughed up blood. This is a sign of internal damage, that being done by Susanoo.
People have also speculated that Itachi's disease was tuberculosis, which is a lung disease. For those who may not know, Tsukiyomi and Amaterasu were born from Izanagi's eyes while Susanoo was born from his nose. So is it a coincidence that Susanoo may damage the lungs while Tsukiyomi and Amaterasu damages the eyes?
Susanoo stemming from the body would also explain why Itachi and Madara were able to use it while blind.
Susanoo IS the disease.