This idea is partially inspired by memories of an old pen plotter at an engineering firm where I worked while in school.
Has there been consideration of designing a fairly uniform standard set of toolheads with docking stations at the sides of the work area. Even now they could consist of several extruders for the different plastics. Eventually there could be welding heads, CNC cutters and routers, negative support material extruders, etc.
If the machine was able to switch heads automatically this could allow construction of complicated devices without constant supervision. For example a few layers of plastic could be extruded, then the router bit could smooth the internal surfaces and more layers could be deposited to create something like a waterpump manifold.
If the attachment was standardized different experimenters could create their own toolheads and share them with others.
The pen plotter with its selection of ink pens, felt pens and maybe an x-acto blade was limited to only storing tools in one dimension. The reprap could theoretically park tools on four sides.
Things like this will be necessary before the reprap is able to create something like a bicycle. Actually it's interesting to consider that mp3 players and probably laptops will be created with repraps before someone makes a bicycle.
