Many concrete elements are typically designed to have reinforcement bars (rebars), so it would be useful if Revit allowed for automatic rebar logic in both System and Loadable families. If this were implemented, all structural elements with concrete properties would automatically be able to accommodate rebar assemblies. While I do not have a specific vision for how the UI should look, I trust that Revit's software engineers and designers will be able to implement this functionality in future versions of the software.