Working for a civil engineering firm I think it would be great if CityEngine could be used as a way of modeling underground infrastructure, such as: sewer networks and water distribution.
CityEngine looks to be an awesome visualization tool with great detail. Having the ability to pull in attribute data from GIS utilities and have it displayed in such a rich environment I think would provide a great way for municipalities and private companies alike to 'see' their infrastructure and how it is related in 3D space.
Some of the key fields I can think of to start with in building a working model would be:
StructureID - unique ID of structure
Rim Elevation - elevation at top of structure
Structure Depth - depth of structure
Invert Elevation - elevation at bottom of structure
Structure Diameter - diameter of structure
Structure Material - material of structure (ex: concrete, brick, block, wood, etc...)
Pipe Diameter - diameter of pipe
Pipe Material - material of pipe
Upstream Pipe Elevation - elevation at upstream end of pipe
Downstream Pipe Elevation - elevation at downstream end of pipe
PipeID - unique ID of pipe
Surface - import from TIN, DEM, contours, etc...
These are just some of my quick thoughts on the subject, but I think having the ability to visualize an underground network in such a detailed and rich environment like CityEngine would be something that is unlike anything out there right now.