`roamingStorage` as a relative to `localStorage` sort of like Windows' "Local App Data" versus "Roaming App Data' would be nice to have in theory.

Of course even if you kept it to the simple KV store interface like `localStorage` you'd need to define sync semantics and conflict resolution mechanics.

Then you'd have to solve all the security concerns of which pages get access to `roamingStorage` and how it determines "same app" and "same user" to avoid rogue apps exfiltrating data from other apps and users.

It would be neat to find an architecture to solve such things and see it added as a web standard.