I wanted to add what seemed a simple enough relationship property to an EditableRoot object but have come unstuck at the first hurdle.
An example would be an editable Project with a read only ProjectStatus, the project is editable and so is which status is assigned but not the status itself.
I can see three scenarios but each one has it's own negative effects.
EditableRoot contains ReadOnlyRoot property - roots are not supposed to own other roots
EditableRoot contains ReadOnlyChild property - the read only object is not a really a child object
EditableRoot contains Id of ReadOnlyRoot and has a reference to a ReadOnlyRoot - Id could be set to an invalid value and would require extra checks to ensure it existed.