I'd like to add that Air Canada's current practice, if I understood correctly, is that musicians will be allowed to pre-board. I think that we have all seen many things put into overhead compartments that could easily be put under seats.
It's a question of balance. When you're talking about something so extremely valuable that even putting it in a pressurized cabin, like animals.... We've heard of animals being harmed in pressurized cabins. It's part of your life. It's your soul, and you want to keep it as close to you as possible.