The bottom layers with assembly lines are extremely reduced in relative height. They are just made high enough so that one can see that the bottom layers significantly deviate from the layers above.

The convergent assembly steps are kept unpractical small (x4) instead of more useful but slower (x32). This way two steps can be shown at once without excessive size of the plastic model.

The number of only three convergent assembly steps above the assembly line bottom layers is realistic but can be extended with purely optional steps.

Intermediate logistic and vacuum lockout layers are omitted.

All internal robotics are omitted - since there as much possibilities to do assembly as there are robots and 3D printers.

Space for factory controls is in the walls.

Infos about such Systems can be found in Nanosystems (chapter 14)  

http://e-drexler.com/d/06/00/Nanosystems/toc.html

OpenSCAD version 2014.10.02