When I first saw this, I appreciated the nobility of the idea but felt a little dismay as it is something I thought would be hard to convince the mobile manufacturing industry to get on board with. I saw it as the type of concept that makes for great BBC viewing when it is trashed and thrown out of the window in the Dragon's Den.
However, Motorola has just announced a new project called Ara which is the realisation of exactly what Dave proposed. The vision is to do what Android has done for the software industry and bring open source modular hardware customisation to the smartphone market, and allow users to control the style, cost, and performance of their phones as they see fit (and ultimately reduce the size of hardware graveyards).
Stay tuned for an alpha release of the MDK (Module Developer's Kit) this winter.