Story idea

Maybe it was done already, maybe not, but here's the idea: shining armor and twilight switch places, so he's the younger brother and she's the older sister.
Every mayor event happens to the other one, so Twilight ends up with cadence, while shining hatches spike and goes to Celestia's school and so on.
Their personalities, however, stay the same.

So the AU would mostly be retellings of the episodes with shining armor instead of twilight, showing how his personality might change things