I might add in some default samples if someone can suggest good ones with a suitable license? That said I believe this is exactly how a MPC would work, i.e. no sounds loaded when it is powered on!
Sure, the problem is 99.999% of people don't have small cut up mp3's ready to go. Making your project useless to us because we'll never see how it works!
I couldn't care less if you close the tab. It's a technical demo of the new W3C AudioContext API. Why don't you create something notable instead pontificating what people want?