You can already do this using things like the Chrome Storage APIs (obviously chrome only, and you need to be signed in, and bundle an extension)
https://developer.chrome.com/docs/extensions/reference/api/s...
https://developer.chrome.com/docs/extensions/reference/api/s...
> If syncing is enabled, the data is synced to any Chrome browser that the user is logged into. If disabled, it behaves like storage.local. Chrome stores the data locally when the browser is offline and resumes syncing when it's back online. The quota limitation is approximately 100 KB, 8 KB per item.