One idea could be revealing the true identities of the other agents in the spy organization that Twilight is part of. Maybe there's a hidden backstory about how they all got recruited and what their real motives are aside from the main mission.
It might also be Anya herself. Since she has telepathic powers, she could accidentally let something slip while reading someone's mind. Or she could be tricked into revealing a secret by someone who realizes she has this special ability. This would create a lot of drama and conflict within the family as they try to deal with the consequences of the secret being out in the open.
Fanfiction.net also has a decent selection. You can find some Spy x Family fanfics there that deal with reveals. However, the interface might not be as user - friendly as AO3 when it comes to filtering, but with a bit of searching, you can still come across some interesting reads.
Well, Spy x Family fanfiction can be really interesting. Some fanfictions might explore different relationships between the characters in more depth. For example, they could focus on the bond between Anya and Loid in a new situation that wasn't shown in the original manga or anime. It's also fun to see how authors play with the spy and assassin themes in unique ways.
Spy x Family manga has wrapped up. It provided a conclusive and fulfilling storyline that wrapped up all the loose ends. Now you can binge-read the entire series without any interruptions.