Allowing orthogonal reference planes as ASSIGNABLE constraints for objects would allow for elements to host to reference planes like levels without the need for additional LEVELS which interfere with view templates view depths:
1. Corresponding Reference pane subcategory - "Walls:" in thie example, a "GLOBAL" subcategory is visible in all categories to help with filtering.
*or a "GLOBAL" available to all categories
2. Create reference plane:
3. "Global" and "walls" show up under constraint options. This one is an example for "Walls"