ID in stages.
The conventional and convenient fixed structure of any given project. As it were.
Conventionally speaking, Industrial Design contributions start with concepting (After the "definition" of the product has been completed). After concept choice follows a cross-stream design phase in which the actual product design is completed. Finally, some fine tuning is done as per the manufacturer's feedback.
Normally and formally, this works well enough. And yes, NRE costs other than design tend to be quite significant in any given product development program, so clearly defined milestones have their virtue.
The waterfall structure with it's milestones and approval gates structures a project. BUT - it tends to reduce transparency in the definition phase, say, if there are unclear or contradictory items in the req' material. Also, it tends to limit the freedom of creative and associative exploration during concepting, since the deliverables are agreed upon prior to the work. furthermore, it pretty much eliminates the possibility of going back and revising fundamental design aspects during the productization phase. so despite of being aware of all the physical limitations of organizing a program, one is left wondering what is being missed out on.
The prototype is the product.
As prototyping technologies develop, maybe initially in small series production, the project could follow lean principles more closely. Essentially a prototype would be iterated in a rapid loop - until it can be called "done".
Build a prototype, learn, go back and build a better one.