This would make cloud vendors kind of like banks. The cloud vendor is holding a kind of property for the user in the user's account. The user would have clearly defined rights to that property, and the legal ability to call this property back to themselves from the account.

This calling back might amount to taking delivery. In a banking context, that is where the user takes delivery of whatever money and other property is in the account. In the cloud vendor case, this would be the user receiving a big Zip file with all the contents of the account.

Taking delivery is not always practical and is also not always desirable. Another option in a financial context is transferring accounts from one vendor to another: this can take the form of wiring money or sometimes involves a specialized transfer process. Transferring the account is probably way more useful for many cloud services.

This leads us to a hard thing about these services, though: portability. Say we delineate a clear property interest for user's in their cloud accounts and we delineate all of their rights. We have some good interests and some good rights; but what does it mean to take delivery of your Facebook friends? What does it mean to transfer your Facebook account from one place to another?