The secreat Itachi gave Naruto I believe this being the logical solution wont be revealed until either:
1. He fights Sasuke again and Sasuke uses Susanoo which is ineffective or deactivated by Itachis powers....or one or all of Itachis techniques passed on are redundant.
2. Like when Sasuke couldnt control Ameratsu at the sight of Madara's Sharingan it could be the same for Naruto If Madara reveals his Sharingan Itachis secret might help Naruto defeat Madara.
BUT I believe the secret will mainly relate to Sasuke as before Itachi gave the power he needed to make sure Naruto would do everything to bring Sasuke back alive so I believe 1 is the logical choice.
1. He fights Sasuke again and Sasuke uses Susanoo which is ineffective or deactivated by Itachis powers....or one or all of Itachis techniques passed on are redundant.
2. Like when Sasuke couldnt control Ameratsu at the sight of Madara's Sharingan it could be the same for Naruto If Madara reveals his Sharingan Itachis secret might help Naruto defeat Madara.
BUT I believe the secret will mainly relate to Sasuke as before Itachi gave the power he needed to make sure Naruto would do everything to bring Sasuke back alive so I believe 1 is the logical choice.