The behavior I'm imagining is: someone sends me a link to a song, provided by their music service of choice, which I can't use. I click the link, then my OS tri

The behavior I'm imagining is: someone sends me a link to a song, provided by their music service of choice, which I can't use. I click the link, then my OS tries to open that resource in my preferred music player. I haven't thought about what happens if that doesn't work (not available on the service for example). You're probably right that it would end up being more clunky and broken. But I think a song is much closer to a resource (like a hyperlink to a website), than to a contact address (like a mailto link). This is actually a regular problem for me, and I solved it by backing up my messages, then using a script to scan them for music URLs, and create a playlist on my music service of choice. It felt like a pretty silly thing to create.