Thank you, @tfa, these are really interesting proposals and use case. I need some more time to think about them, but especially the idea of using keys to divide a bigger entity into smaller is an interesting approach.
At this very moment we have only modelled MData with the idea of creating share-ability for multiple apps (hence the name appKeys at some places) and restricting on a feature level (rather than on a per-key-level) with the shared-folder-of-pictures-idea in mind. But you certainly raise some interesting features.
I am wondering if it’d be possible to have a high-level abstraction emulating of this behaviour on top of the currently proposed MData first though. That’d make it easier for us to test this and built some concrete use cases to gain a better understanding and more insight of the actual requirements of such a solution (before trying to built it into the network). What do you think would be a simple real world example that could be developed as an app and might be possible to test such an emulation?