It depends on the price, and whether or not it would catch my kid's attention. I can say that my five-year-old wouldn't care less about it now because it doesn't look like a robot, but it could be something useful for my baby daughter as she gets more playful in the bath. While the color-changing function is great, it wouldn't be worth it for that alone if my daughter just completely ignored it. My guess is that the main market would be to people putting together gift baskets for baby showers, because it's cute and useful, but that also means that the price would be a pretty big factor.
As for playing music -- I think that's an unnecessary addition, and that it would be very difficult to keep from getting water and gunk in the mechanics, and consequently rust, so it would likely give out pretty soon anyway. Kids that are young enough to enjoy a duckie are probably also ones that a parent wouldn't want to take both hands away from long enough to wind it up, and bath time is more for splashing and bubbles anyway. Personally, I think this is a feature that would just add cost and that not many people would like.