A really interesting plot twist could be that Vernon Dursley is forced to work with the wizarding world to save his own skin. Maybe there's a threat that endangers not only the wizarding world but also the Muggles, and Vernon has some unique knowledge or ability that can help. This would be a huge change as he has always been so opposed to the wizarding world. He would have to learn to cooperate and respect the world he once despised.
Most of the Harry Potter fanfics that touch on Vernon Dursley's comeuppance are more about him being made to understand how wrong he was. In some stories, magic might be used to make him experience the fear and isolation that Harry felt in his house. For instance, he could be magically trapped in a small space, similar to how Harry was locked in his cupboard, which gives him a taste of his own medicine. But again, this is not torture in the cruelest sense but more of a moral lesson.
Redemption is also a popular theme. Writers often like to give Vernon a chance to make up for his years of mistreating Harry. They might show him gradually changing his views and actions towards Harry as he realizes the error of his ways. Another theme is the clash between the Muggle and magical cultures through Vernon's eyes. His strict adherence to Muggle normalcy makes for an interesting contrast when faced with the chaos of the magical world.
One interesting fanfiction could be about Vernon Dursley having to face a magical threat in the Muggle world on his own. He might have to rely on some of the little knowledge he has about the wizarding world through Harry. Another could be a story where Vernon and Harry are forced to work together during a crisis that affects both the Muggle and wizarding communities, changing their relationship completely. There could also be a fanfiction exploring Vernon's past and how it might have influenced his treatment of Harry, and then how things could have been different if certain events in his past were changed.
One interesting fanfiction could be about Vernon Dursley's perspective during the time when Harry first received his Hogwarts letter. It might explore his extreme reactions and the inner turmoil he felt at the thought of magic being real. Another could focus on a situation where Vernon has to interact with the wizarding world in an unexpected way, like when he accidentally stumbles into Diagon Alley.
One great Vernon Dursley fanfic is 'The Unseen Side of Vernon'. It delves into his character in a unique way, showing his insecurities and how his upbringing might have shaped his rather unpleasant personality towards Harry. Another one could be 'Vernon's Redemption Arc' which is an interesting take on him trying to make amends for his past behavior towards Harry.
There might be some out there, but it's a rather unusual pairing considering Vernon's often cruel treatment of Harry in the original series. Fanfiction can take all sorts of creative turns, though. You could try searching on popular fanfiction websites like Archive of Our Own or Fanfiction.net. However, this pairing goes against the typical relationship dynamic presented in the Potter books.
I'm not really into slash fanfiction myself, but you could try searching on some popular fanfiction websites like FanFiction.net or Archive of Our Own. There might be some unique takes on the relationship between Harry Potter and Vernon Dursley in those platforms.
One great fem Harry Potter and Vernon Dursley fanfiction is 'A Different Perspective'. It explores how a female Harry Potter might interact with Vernon in a more complex way than in the original series. The author really delves into the characters' personalities and how they would clash or, surprisingly, sometimes find common ground. It's an interesting read that gives a fresh take on the relationship between these two characters.
One interesting story could be where Vernon Dursley has a sudden change of heart towards Harry Potter due to some magical influence in the fanfiction. Maybe he starts to see Harry's value and tries to protect him from other dark forces in the wizarding world. This would be a great twist on their usually antagonistic relationship.
Perhaps Vernon Dursley sells Harry fanfic to get back at the wizarding world that he despises. He might think that by spreading false or embarrassing stories about Harry in fanfic form, he can somehow undermine the reputation of wizards. For example, he could write fanfics where Harry is shown as a bumbling fool, completely different from the real heroic Harry. However, this backfires as the wizarding world sees it as a comical attempt by a Muggle and it actually makes Harry more popular as they rally around to defend him.