Cool. So in my mind I was thinking that VisualizationFrame's would be in the background. One would use them explicitly if they were doing some general animation, but if you were doing an animation with a rigid body system, when you initialize a visualization/animation, these could be created automatically. 

It seems that we are thinking about VisualizationFrame different, since you are adding bodies and particles to a single VisualizationFrame. Maybe you are thinking of VisualizationFrame the way I'm thinking about MultiBodySystem, or as a manager class for visualization ("VisualizationManager")? In which case, I'm not sure how it differs from Scene. I hope to understand better what you're thinking of.

This might be easier if all rigid bodies, particles, were part of a manager class like MultiBodySystem.