It would be great if ESRI could incorporate system dynamic ideas into ArcGIS. Many of the programs used out there: Powersim, GoldSim, Vensim and Stella don't have a good way to interact geospatially without using an expensive SDK (offered only be a few). We are always reducing and analyzing data, then exporting to a .dbf, then into an excel file so the model can use the data. Or, coming up with a very complicated way (in KML) of displaying a linked output to something like Google Earth using network links. Since ESRI now has the ability to do time based analysis and simulations, it would be a good time to start looking at incorporating system dynamic methods into Model Builder and ArcToolbox.