A possible plot is that their baby is born with a prophecy attached to it. The wizarding law dictates that any baby with a prophecy must be placed under special protection and observation. Draco and Hermione, being protective parents, try to find a way to ensure their baby's normal upbringing while still adhering to the law's requirements. This could lead to a lot of drama and character development as they face opposition from those who strictly enforce the law.
Maybe the marriage law causes a stir in the wizarding world. Draco and Hermione initially resist but then realize that for the sake of the baby, they need to make it work. The baby might be born with a special gift that is a combination of the Malfoy and Granger magic. They could have to deal with Draco's family not accepting Hermione at first, but the baby becomes the bridge that brings them all together in the end.
One idea could be that Draco and Hermione's baby has unique magical abilities that draw the attention of both the wizarding world's good and bad elements. The baby might be able to communicate with magical creatures in an extraordinary way, leading to adventures where they have to protect the baby from those who want to use its power for evil.
Well, a great plot idea could be that they are paired by the Marriage Law and have to pretend to be a happy couple in public for some political or social reasons in the wizarding world. But in private, they are constantly bickering. As time goes on, they find that they can't help but fall for each other. They might also face challenges from Draco's old Death Eater associates who don't approve of his union with Hermione.
One idea could be that the marriage law forces them to live together and they initially clash due to their different backgrounds. But as they get to know each other's true selves, they start to respect and even fall in love. For example, Hermione might introduce Draco to the value of Muggle - born magic and he could show her some of the more complex pure - blood magic traditions in a new light.
Another plot could be that the baby project is a ruse by the teachers to get Draco and Hermione to reconcile the differences between Slytherin and Gryffindor. As they take on the project, they start to understand each other's houses better. The 'baby' becomes a symbol of unity for them, and they eventually fall in love while trying to raise it in the best way possible.
One idea could be the baby having a special magical ability that Draco and Astoria have to figure out how to handle. For example, the baby might be able to communicate with magical creatures from a very young age. Another plot could revolve around the baby being in some sort of danger, like a dark wizard targeting the family because of Draco's past. Or perhaps the baby's first year at Hogwarts, with Draco and Astoria being overly protective and the comical situations that arise from that.
One idea could be that Harry and Draco find an abandoned magical baby and they have to work together to take care of it. This forces them to put aside their differences and learn about each other in a new way.
One idea could be that their child discovers a hidden magic that neither of their parents were aware of. This magic could be a key to solving an ancient mystery in the wizarding world. Another plot could be the child having to navigate the social difficulties of being the offspring of two former rivals, facing prejudice from some pure - blood families who still hold grudges against Hermione for being a Muggle - born.
One plot idea could be that Draco and Hermione are rival CEOs in the wizarding business world. They start off hating each other due to their different management styles and company loyalties. But then, they are forced to work together on a project to save the wizarding economy. As they spend time together, they begin to understand and respect each other, and eventually fall in love. Another idea is that they are co - CEOs of a newly formed, progressive wizarding company that aims to bridge the gap between pure - blood and Muggle - born wizards in the business realm. Along the way, they face opposition from traditionalist wizards but they fight it together and their relationship deepens.
A possible plot is that Draco, who is in Slytherin, discovers a hidden secret about Hermione's family that has ties to Slytherin. This makes him see her in a new light and they start to form an unlikely alliance. They could then face challenges from their respective houses. Another plot idea is that in an alternate universe, Hermione is sorted into Slytherin and she and Draco become friends and then something more, as they strive to change the negative perception of Slytherin from within.