I think young Sasuke would have a very intense reaction. He was so consumed by his hatred for Itachi at that young age. A Sasuke vs Itachi fanfiction would be like a trigger for him. He would be eager to see how the fictional fight is portrayed. If Sasuke in the fanfiction is shown as strong, it might fuel his own ego and make him strive even harder to become powerful. However, if the fanfiction shows Itachi as superior, it could enrage him. He might feel that it undermines his own goal of defeating Itachi and he might even want to find the writer to correct their 'wrong' view.
One common theme is power. Since Kyuubi is a powerful entity, many fanfics explore how Sasuke either gains power from it or has to deal with the overwhelming power of Kyuubi. For example, some stories show Sasuke learning to harness Kyuubi's chakra in unique ways.
A theme that also pops up is the struggle for control. Sasuke might be tempted by the power of the kyuubi and there could be a struggle within him on whether to embrace it fully or resist it. This internal conflict adds a lot of depth to the stories and makes for an interesting read as the reader wonders which way Sasuke will go.
I like Naruto in these fanfics because he always stays true to his beliefs. He is constantly trying to bring Sasuke back to the village and is willing to fight for their friendship.
One of the best moments is when they have a rematch that showcases their growth. Naruto has become stronger with his new jutsu, and Sasuke has further mastered his Sharingan powers. The intense battle of ideologies during the fight is captivating.
Well, Naruto has a great advantage here. When it comes to Kyuubi Naruto, he has access to an incredible amount of chakra. This allows him to perform powerful jutsus and endure long battles. Kiba, on the other hand, depends on his Inuzuka clan techniques which are more physical and based on his partnership with Akamaru. Against the might of the Kyuubi, Kiba would find it extremely difficult to land a decisive blow. So, it's most probable that Naruto would emerge victorious.
A common theme is identity crisis. Sasuke suddenly being a girl would make him/her question who they are now. Another theme could be acceptance, both from Sasuke herself and from the other characters. Also, there might be a theme of newfound friendship. As a girl, Sasuke might make new friends that he wouldn't have made before.
It really depends on the writer's preference. Some fanfictions might have Naruto winning because of his unwavering belief in friendship and his ability to draw on the power of the nine - tails. Others might have Sasuke winning due to his strategic mind and mastery of the sharingan.
It's not clearly stated in the original Naruto series that Konoha as a whole watches Naruto vs Sasuke fanfiction. Fanfiction is a creation of the fans outside the official story. However, it would be an interesting concept to think about. Some characters might be amused or even inspired if they were to read such fan - created stories, but there's no in - canon evidence for it.
One common theme is unrequited love. Sakura often has strong feelings for Sasuke, but Sasuke may be too focused on his own goals to fully reciprocate. Another theme is the power struggle. Since they are both powerful ninjas, their battles can represent a struggle for dominance or recognition within the ninja world.