I don't notice any authorization model in this, where (for example) you could grant a service read/write on a portion of your data but commit yourself to read-o

I don't notice any authorization model in this, where (for example) you could grant a service read/write on a portion of your data but commit yourself to read-only access. But maybe it's in there, or possible. If that were a part of the conventions, or even if it isn't, services could sign their own versions of data in legal states – as with signed/encrypted cookies. Then out-of-agreement edits could be detected, and possibly rejected as errors, rather than causing other surprises. (This could make for some ugly partial-failure/unexpected-state cases, though.)