A really interesting plot twist could be that killing Voldemort early somehow disrupts the balance of magic in the wizarding world. Maybe dark magic starts to seep out in unexpected ways and Harry has to deal with the consequences of his actions in a way he never expected. For example, spells start going haywire and he has to find a way to fix it all.
One popular 'Harry kills Voldenmort early' fanfiction is 'The Early End' on FanFiction.net. It has an interesting plot where Harry discovers a new spell that gives him the upper hand early on.
There are indeed some. One reason for the existence of such fanfics could be the desire of fans to see a different outcome earlier in the story. For example, in some of these fanfics, Harry might use his connection with Voldemort in a more aggressive way to end the Dark Lord quickly. It gives a fresh perspective on the whole Harry Potter universe and can be really interesting to read.
You can look for them on Archive of Our Own. It has a large collection of Harry Potter fanfics, and you can use relevant tags like 'Harry kills Voldemort early' to narrow down your search.
In the fanfiction, there could be a range of consequences. On one hand, he could be seen as a hero by his fellow students. They might admire his bravery and his ability to take on a dangerous troll. However, the teachers may be more cautious. If Harry used excessive force or magic that was not in line with the school's code of conduct, he could be given detention or even face a disciplinary hearing. Also, depending on how the troll was killed, there could be some magical fallout. For example, if he used a very dark spell, it could have an effect on his own magical core or his relationship with magic in general. Moreover, the death of the troll might also attract the attention of other dark creatures or forces that were somehow related to the troll, putting Harry in further danger.
One consequence could be that he becomes a hero among his peers. Everyone in Hogwarts might look up to him even more. The other students could see him as a real dragon - slayer, which gives him more popularity and respect.
There could be. Fanfiction is a platform for fans to experiment with different plot ideas. Since there is a lot of tension between Harry and Lucius in the original books, some writers may have been intrigued by the idea of Harry killing Lucius. You can search on popular fanfiction websites to see if such a story exists.
After Harry kills Voldemort in the graveyard in the fanfiction, the magical balance might shift. With Voldemort gone, some of the dark magic that was prevalent might start to fade away. The Hogwarts School of Witchcraft and Wizardry could see a new golden age. New spells and magical theories might be explored as the fear of Voldemort no longer holds back the wizarding scholars. Harry himself might start to travel around the world to spread the news of Voldemort's defeat and also to learn more about different types of magic. His friends would also have new opportunities, like Hermione might be able to further her studies without the constant threat of Voldemort and Ron could finally relax and enjoy a more peaceful life at the Burrow.
One consequence could be that he becomes a hero among the wizarding community. People start to look at him with even more admiration and respect. His reputation as a powerful wizard grows even stronger.
He might gain more respect from his peers. After all, killing the Basilisk is no small feat. His friends would probably look up to him even more, and his reputation in Hogwarts could soar. He could also become a bit of a legend among the younger students.