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.
A fanfiction could also be set in a scenario where older Sasuke and young Naruto are accidentally sent to a different dimension. In this strange new world, they have to rely on each other to survive. Sasuke's calm and calculated nature combined with Naruto's boundless energy and optimism would make for an interesting dynamic. They'd have to find a way to get back home while also dealing with the unique challenges of this new dimension.
One great 'Sasuke Young Justice Fanfiction' is 'Sasuke in Young Justice: A New Alliance'. It has an interesting plot where Sasuke's skills blend well with the Young Justice team's dynamic. Another good one is 'Sasuke's Journey in Young Justice'. It focuses on how Sasuke adapts to a new world and new allies.
You can start by looking on Fanfiction.net. It has a large collection of fanfictions, and there are likely to be quite a few 'Sasuke Young Justice' ones there. Another place is Archive of Our Own (AO3). It has a great tagging system that can help you find the specific fanfictions you're interested in.
One common theme is revenge. Since Sasuke is driven by revenge in the original series, many fanfictions about young Sasuke explore his thoughts and feelings regarding revenge at an earlier age. For example, how it starts to consume him even as a young boy.
Staying true to the Naruto universe's lore can be a challenge. There are many established facts about their relationship and abilities. If you deviate too much, it can feel out of place. For example, if you give Sasuke a power that doesn't fit with the chakra system in Naruto, it might seem off.
He might feel anger. Since he was so set on revenge against Itachi, any portrayal that didn't match his view of himself as the victor could make him angry.
One possible plot could be that Naruto and Sasuke take on a young protege. They might start by teaching the basics of chakra control. Naruto could show how he mastered his own unruly chakra, while Sasuke would focus on precision and discipline. They could also train the young one in combat, with Naruto's unorthodox yet effective fighting style and Sasuke's refined and powerful techniques. Eventually, they might enter the young one in a local ninja tournament where they face off against other talented young ninjas.
One popular theme is friendship. Since Naruto and Sasuke have a complex relationship, many fanfictions explore how their friendship develops during their youth. Another theme is rivalry. Their competitive nature towards each other is often delved into. Also, the theme of self - discovery is common. As they are young, they are still finding out who they are and fanfictions might focus on this journey in the context of their relationship.
Well, 'Sasuke's Early Days' is a popular one. It portrays young Sasuke's training, his thoughts during that time, and his dreams. It's a great read for those who want to understand more about Sasuke's early life and how it shaped him into the character we know later on.