So far I've got the following in a working state:

* One-click autoscaling Navidrome deployment per user

* 100GiB+ distributed storage per user (configurable)

* unique Subsonic endpoint per user instance

* autocreated admin credentials

* custom upload webinterface for music library (takes zip & folders)

* automated tagging of all uploads using musicbrainz API

* tested backup & validated restore

I'm curious if anyone would be willing to pay for such a service?