So if you're trying to look for someone to cast in an Animated Series story, listening to a voice sample would help you determine your choice! Also, I hope the voice samples not only include the Celebirty, voice actor or singer's actual voice, but also includes some voice roles they did in various projects!
You have a point there, if they are trying to find what they're searching for, then this might be the solution to most of this site's problems. I mean we don't even know what their voices sound like.
Although, I do have a solution on how they can add this. There is this website called 'BehindTheVoiceActors', which includes voice samples for characters that certain voice actors or celebirties voiced. Maybe if MyCast works with BehindTheVoiceActors, maybe thy can make adding the feature easier! Although time will tell :D