Sona doesn't make any sense as a member of the crew
The entire crew of the Morning Star is full of character and identity. Jinx is the crazy daredevil pilot, Yasuo is the stoic, lonestar captain. Malphite is the gentle big guy mechanic with a bit of a temper but he means well. Kayn is the crazy guy hellbent on revenge. What on Earth is Sona (who basically has no character whatsoever) doing here? Why would a mute be on the crew of a ship? What is she doing there? What does she contribute to the crew's dynamic? So many other champions would have been a great character to add to this over-the-top AU (It kind of reminds me of Wildstar, actually), but instead, they choose one of the most bland, boring, and basic champions in the game. Even the Ziggs skin, which wasn't in the trailer, fits. Ziggs is full of character and fits perfectly into this goofy setting.
I know you want to sell skins Riot, but there's already one for Jinx, Yasuo, and Kayn. Isn't that enough to get your guaranteed sales? Do you really have to shamelessly plug Sona in just to make more money?