Tell that to my mother. I'm serious here: it's easy for you and me -- heck, I'd just collect it via DBus, reverse Spotify's local storage or scrape it from the web player. But that takes effort and expertise, something very few people on this planet are both capable of and willing to do, unless it's clear that the service is going out of business soon. Furthermore, hacky exports like this will not be importable on other services either.

So make a service that emails people their saved albums. Send monthly incremental updates. Their backup storage will be their inbox, and restoring the data to a new service will be a couple hours manual clicking and typing.

The hard part is explaining to our mothers that their music app might become unavailable, that they should care about this, and that they should take action to mitigate the effects.

But on the other hand, consumers get locked in all the time, and civilization hasn't collapsed yet.