Seriously, I had my MP3s organized this way pre-iTunes. I get why that can’t scale to the general public, but I still think a tool could approximate it.
For one thing, even if this was a good idea, you would still need a tool to covert the meta information from the ID3 tags that come with your music from amazon, iTunes Store, or wherever into a myriad of hard links.
Further, it's hard to imagine how the hard link system could ever be as flexible as even an average music library program, where you can trivially find songs released between 1990 and 1995, with at least one play count, and then have them sorted by beats per minute.
Music libraries act as relational databases, which are a far more powerful data modeling tool than the file system.
Seriously, I had my MP3s organized this way pre-iTunes. I get why that can’t scale to the general public, but I still think a tool could approximate it.