If I wrote My Little Pony fanfic it would be Luna/Applejack friendship, because Luna is the one I identify with the most and Applejack is somepony I would love to be friends with.

Since Applejack's theme is Honesty, the story would be about what really happened before Celestia banished Luna to 1000 years of solitary. I don't believe the victor's history. Maybe Luna needs help even remembering the truth, let alone processing it.