"A Glee AU role-play that swaps the personalities and histories of its canon characters with each other."
now see, i love the idea of it, but swapping the personalities of the characters? what's the point in that?
a better idea would be swapping the histories of characters while retaining their personalities. What would have changed? How would they react? How would that affect their relationships and interactions with the other characters? now THAT would be a fantastic prompt.
(unfortunately this requires a firm grasp on characterization which i think is out of reach for most tumblr role-players.)