One possible plot development could be Harry finding a new magical family or community that accepts him wholeheartedly. Maybe he discovers a hidden magical society that has been observing him at the Dursleys and now offers him a real home and proper magical training.
Another plot could be that as Harry leaves the Dursleys, he gets involved with a group of outcast wizards. Together, they form a sort of misfit magical gang that challenges the norms of the wizarding world. They might use unorthodox magic to solve problems and in the process, Harry learns that there's more to magic than what he was taught at Hogwarts.
Another plot development could be that the Dursleys try to keep Harry's magic a secret from the wizarding world, fearing they will lose him. But as Harry grows older, he starts to find ways to reach out to the magical community on his own, like making friends with a stray magical creature that finds its way into the Dursleys' backyard.
Well, in this kind of fanfiction, it might be that Harry is adopted by a wizarding family from another country. This new family could introduce him to different magical cultures and traditions. He could learn spells and magical techniques that are not known in the British wizarding world. Also, he might start to explore his own identity without the shadow of the Dursleys. He could find out more about his parents from this new family's perspective and gain a new understanding of his place in the wizarding world.
Well, in this kind of fanfiction, a plot development could be that Ginny, being pregnant, discovers new magical abilities or powers related to motherhood. This could be a unique take on the story. Also, the wizarding community might react in different ways to Ginny's situation. Some could be supportive, while others might shun her because of Harry's departure. It could lead to Ginny having to fight for her place in the community and prove that she can be a great mother on her own terms.
One possible plot development could be that Harry discovers his magic earlier on his own due to the neglect. He might start exploring the wizarding world secretly, finding hidden magical artifacts in the neighborhood. Another could be that he forms an unexpected alliance with the local magical creatures that sense his isolation. Maybe he even starts teaching himself basic spells from an old, dusty spellbook he finds in the attic.
Another plot could be a time - travel scenario. Harry goes back in time and tries to understand his early years with the Dursleys better. He might try to change some of the negative interactions and make them more positive, like showing Dudley that there's more to life than bullying.
One idea could be exploring how the Dursleys react when Harry starts to show signs of magic before he even goes to Hogwarts. Maybe he accidentally makes Dudley float during a family dinner.
The plot could be that Harry's parents are in a magically-induced coma. The Dursleys are tasked with looking after Harry until a cure can be found. Harry might feel a sense of isolation as he is with the Dursleys but constantly thinking about his parents. He could start to show early signs of magic, which terrifies the Dursleys even more, but also gives him hope that he can somehow use his powers to wake his parents up.
One interesting plot development could be how Harry and Daphne first come to terms with their betrothal. Maybe at first they are reluctant, but as they spend time together, they discover they have more in common than they thought.
In some 'Harry Kidnapped by Pettigrew' fanfictions, one interesting plot development could be Harry's struggle to escape. He might use his wits and the little magic he can muster in captivity. For example, he could try to communicate with his friends through magical means that Pettigrew doesn't suspect. Another aspect could be Pettigrew's motives. Maybe he's being blackmailed by some dark forces to kidnap Harry, which adds a layer of complexity to the story.
Well, one possible plot development could be Harry struggling to control his new werewolf nature. He might have to deal with the stigma within the wizarding world. For example, some might fear him or treat him differently. Another aspect could be his relationships changing. His friends might be initially shocked but then try to support him in finding a way to manage his condition. Maybe he also discovers new powers or abilities related to his werewolf side that he has to learn to use properly.