I poked at this for quite a while. Problem with not creating widgets is that the code for rendering frame decorations wants to use views. That is, it wants to use views for painting, for hover effects, for actions, for updating cursor... It's not terribly complex to get a View to paint outside a widget, but the event dispatching is a bit hairier, and would result in needing to duplicate a fair amount of code (or some refactoring between Widget & RootView).
While the current situation of using Widgets on both ends is mildly confusing, it dramatically simplifies things. So, I'm going to leave it as is and close this out.