I have exactly the same plan as yours 
BTW, arch sections can already have 2D objects. I also plan to extend the BuildingPart to have an implicit, “embedded” section plane. So you would basically have three objects to work with, to deal with views:
- Section planes: do not contain objects, define a 3D view (not yet), define a 2D view
- Building parts: contain objects, define a 3D view, define a 2D view (not yet)
- WP Proxies:do not contain objects, define a 3D view, do not define a 2D view