We backed up Spotify (metadata and music files). It’s distributed in bulk torrents (~300TB). It’s the world’s first “preservation archive” for music which is fully open (meaning it can easily be mirrored by anyone with enough disk space), with 86 million music files, representing around 99.6% of listens.
It depends on what your goal is: If you want to preserve the music that is important to most people or to the era, you should start with the most popular stuff. And Spotify has a big spam problem. Everybody who thinks he is a DJ wants his music to be on there and there is so much AI music flooding the scene. So it does make sense to backup what people are actually listening and not some AI-generated music spam nobody cares about.
I mean, they say earlier that music is actually well-preserved, but it’s disproportionately popular music. If the goal is then to preserve everything, I’d expect them to go for stuff that isn’t likely to be in some random audiophile’s collection or whatever then.