Alas, this is more complicated than just including a link. The mp3 needs to be served with permissive "CORs" headers, and most are not. I made the call, that it would be too confusing for users to try to support loading from URL.
Yeah, that makes sense. You would have to download the remote resource in the link and re-host it which can get expensive quickly. There are probably a few scenarios where DNS tricks would save the day, but not reliably.
