This will probably never happen, but I'd love to see an event where Hina and Sayo switch bands for a day. Maybe Hina wants to take advantage of the fact that they're identical twins, and (somehow) convinces Sayo to switch places with her and see how long it takes for someone to notice.
Obviously, hilarity ensues. But at the same time, both Sayo and Hina gain an appreciation for the friends their sister has made. At the end of the day, they can reflect on how being in a band has changed them both for the better.
It's a pretty silly idea, but hey, we already had an event about a magical mole from another dimension, and RIMI WITH GUN, so at this point, I don't think anything's that unrealistic.