The whole electronics supply chain is optimized towards volume manufacturing. There's a second supply chain for small volumes, but it's expensive: boards instead of chips or more expensive chips and boards(due to volume breaks), complex development, testing. The assembly costs are relatively minor.

I think the first step for the kinko[1] vision would be to largely automate the development and test costs. Maybe arduino is one path to this.

[1]I think it would make more sense as a centralized source who prints designs coupled with rapid shipping, not as a kinko.