I'm not sure I see the distinction you're making between 3D design and other spatial reasoning tasks. You can use RL to teach navigation or video game play too. Does that mean these tasks are not spatial reasoning? Additionally, 3D CAD is all about understanding how objects "interact with each one another in a highly quantitative way." I mean, not in the rabbit example, but the container Fable designed for me holds around 30 different types of objects. It figured out a way to arrange them that was more space efficient than what I'd originally described. It considered the best way to stack the fasteners in each bin to pack them as densely as possible. It identified the risk that some very thin objects could slide between compartments in transit, and modified the design to prevent that. It correctly solved for the tolerance between objects that needed to snap together. These all feel like understanding how objects interact with each other. The model didn't just talk about these concerns, but created two 3d models for the case and its lid that accurately reflected them. I hadn't seen that before.