Er, what I meant is that Android already does this. All apps' data stores are private to that app by default. The only way for any other app to access them is f

Er, what I meant is that Android already does this. All apps' data stores are private to that app by default. The only way for any other app to access them is for the owning app to specifically set up an interface and permissions to access it, and the accessing app to request those permissions at install time. I don't have much experience with iOS, but I expect it does something similar.