Comment by sam0x17

Yeah, having attempted to operate a service very similar to this (only more focused on general encrypted cloud storage) I will say there are no good economics in usage-based billing. You're much better off selling a license to use the software and give users the ability to use common cloud storage providers (minimally the s3-compatible ones but also things like Google Drive) as the backing for this. Even safer from a legal perspective would be not having accounts at all and allowing users to purchase a 1-year license based on license keys that are cryptographically validated but not stored anywhere. Then it's impossible to do anything user specific whether you are compelled to or not.