I think the key issue with which I am trying to address with this new tool is best summed up when you compare SketchUp (SU) with Chief Architect (CA). Both can be used to model a structure, one is fully parametric but is quite locked down and restrictive while the other is very free form, allowing the user to do as they please. The downside to this freedom is that the program has no way of keeping track or making sense of all these custom changes and hence the parametric ability cannot natively exist.
CA does a nice job of keeping everything well contained but its 3D environment locks the user down too much in my opinion, and for the designer (who is not too different from an artist) who wants to express their creativity, I think this can be too restrictive.
Being able to insert "custom" geometry into the wall, roof and foundation assemblies, whilst categorizing and tracking it maintains the parametrics (and estimating) but also allows flexibility. Being able to retain this custom geometry after a regen is critical to the success of this paradigm.
In a nutshell the plugin is trying to maintain the flexibility of SU while giving the user the parametrics of a program like CA.