One of the tenants of TPS is to learn as much as you can, as quickly as you can, with as much future flexibility as possible. This is the whole point of JIT.
The more quickly something can be built or mocked up, the more quickly it can be tried and tested, and the more quickly we learn what improvements can be made.
We are seeing the beginning of a revolution in fabrication technology as 3D printing starts to move out of high-end prototyping shops and into the mainstream.
This (very entertaining) video tells about an open source(!) 3D printer design that can be had for about a little over a grand. (USD$1250) (makerbot.com)
Open source means that you can grab the technology and scale it if you want to.
The step from one-off prototyping to full mass-customization is a small one. It is just a matter of time. The ultimate die change is none at all.
So – rather than looking at the limitations of this technology, look at the possibilities.