I mean Itachi is dead after all, so his illness won't stop him in a rematch with his brother...
Itachi is far more knowledgeable than Sasuke about the Sharingan in general so I'm almost sure that Itachi might know some of the EMS techniques. However, as smart as Itachi is, I don't think he'll be able to take on EMS Sasuke simply because Sasuke is now too hax. Even when he was at the risk of going blind when he only had MS, Sasuke didn't care. He's going to be spamming his EMS powers excessively now that there is no drawback, that would overwhelm Itachi. I don't think his experience will save him from Sasuke's overwhelming new power. It will probably delay some of Sasuke's attacks though. One thing Itachi could do is talk to Sasuke. I think Itachi is the only person who can maybe change Sasuke's ways.
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