Interestingly enough, there's a precedent for exactly that idea (for Meloetta, anyway). Read this quote from the musician who teaches Meloetta Relic Song in Gen V: "My mother once told me of a Pokemon that played a melody and danced so lightly that it filled people's hearts with joy. Then sorrow darkened the world, and the Pokemon lost the melody... Also, at that time, some red shoes were lost somewhere..." Meloetta sang a lost song and danced. Then it forgot the song and its red shoes were lost. Well, what if we find these red shoes in Gen VI as an item which, if held by Meloetta, changes it to Pirouette form so that it can start battles in that form?