Well, a plot could revolve around their marriage being put to the test when a new villain targets them specifically because they are married. This forces them to work together in a different way than they did before. They might also have to deal with the media attention that comes with being a high - profile married couple in Star City. Also, they could have a disagreement about how to handle Oliver's past coming back to haunt them.
One idea could be them facing challenges in their married life due to Oliver's vigilante duties. Maybe Felicity gets worried every time he goes out at night. Another could be them planning to start a family and all the joys and concerns that come with it. Or perhaps they take a trip together and encounter some old enemies during their journey.
There could also be a storyline where they decide to start a family. This would bring in elements of how they would raise a child in a world full of danger and how their relationship would change and grow with the new addition to their family.
Well, a plot could revolve around Felicity having a difficult pregnancy. Oliver then has to balance his duties as the Green Arrow and being a supportive partner. They could also have a story where they are trying to prepare for the baby's arrival while dealing with a new villain in Star City. This villain could be targeting pregnant women, making Felicity a prime target. So, Oliver has to stop the villain while also taking care of Felicity.
One idea could be that Oliver and Felicity's baby has some sort of unique meta - human ability that they have to protect it from those who would use it for evil. Another could be the baby getting kidnapped and Oliver and Felicity having to team up with their old Arrow - team friends to get it back. They could also face challenges in raising the baby while still being vigilantes.
One common plot idea is exploring their life after the events of the show. For example, how they handle raising a family while still being involved in the vigilante world. Another idea could be alternate universes where they meet under different circumstances, like Felicity being a superhero herself and Oliver being a tech genius who helps her.
Perhaps there's a villain who targets Felicity because of her pregnancy. This villain could see the baby as a way to get back at Oliver. So, Oliver has to go to great lengths to keep Felicity hidden and safe. Meanwhile, Felicity could be using her intelligence to find a way to outwit the villain from her hiding place, all while dealing with the physical and emotional changes of pregnancy.
Another plot could revolve around the challenges of raising a baby in their dangerous world. They have to constantly protect the baby from their enemies. Maybe there are villains who try to kidnap the baby to get to Oliver or Felicity. So they have to set up a super - secure hideout and enlist the help of their friends like Diggle.
One plotline could be their struggles with balancing their superhero/vigilante life and married life. For example, how they keep their relationship a secret from their enemies while still being a loving couple at home.
A third plot idea could be a 'what if' scenario. What if they had their first time under the influence of a meta - human power that made them more open and vulnerable? This could lead to some interesting character exploration as they deal with the consequences of this unexpected event. They would have to navigate their feelings and the changes in their relationship while also dealing with the potential danger of the meta - human's power still being out there.
There are fanfictions where Felicity and Oliver get married and start a family right away. In these stories, they deal with the challenges of raising a child while still being heroes. For example, they might have to balance a baby's nap time with fighting crime. It's really cute to see how they support each other in this new chapter of their lives.
Diggle would be a great addition. He's Oliver's friend and partner, and his presence could add some interesting dynamics to their married life. He could offer advice or be there to help out in times of trouble.