CityEngine users should be able to select data that is taken straight from ArcGIS geodatabases, so network and polygon changes in ArcGIS are automatically updated in CityEngine without needing to go through an import/export data workflow.
It shouldn't be for all the datasets only ones the user chooses, for instance in our industry we will often move a road alignment, I don't want to have reimport that road alignment and create the model again.
This should work in reverse too, so that object attributes set in CityEngine can be immediatley written to and read by ArcGIS. This way the worklfow would be more 'fluid'.
Better yet place all of the CItyEngine features within ArcGIS desktop, so you only need one program open....