But having separate private and personal accounts on your phone is very different from application resource namespacing. They're essentially orthogonal concern

But having separate private and personal accounts on your phone is very different from application resource namespacing. They're essentially orthogonal concerns. In the case you're making, a user (a real actual human user) has different settings when _using_ the phone in two contexts. In the latter case, applications are restricted to sandboxes with well-defined interactions between each other's memory, processes, devices, sockets, and files.