OpenSim/Micropolis
Micropolis
The models could be edited in the above mentioned model editor, maybe the editor could be implemented as a GTK+ widget that could be created right in the Micropolis UI. Turtle Art could be used to define agents like bulldozers, etc, as Don Hopkins has suggested. Time permitting, the SD and Turtle Art editors could be integrated. As Homunq mentioned, this would (at least initially) miss a lot of the core processing done in Micropolis, like graph analysis and agents. I would hope the legwork involved in integrating the simulation engine with Micropolis, along with the work done to integrate GIS into the simulation engine will make the future addition of these additional 'features' easier than they were before. For example, if you can define models for how individual cells in a map behave and interact with adjacent cells, abstracting this a but further to support agents isn't a giant leap. For GSoC, I would like to get Micropolis to use the simulation engine for some of its easier models and calculations, a working proof of concept I can expand upon in the fall.
Micropolis Details
This work will probably fall outside the scope of GSoC, but I think its useful to see some of the applications and future directions of the project. As mentioned, I'm going to use GDAL to interact with raster maps. It will be really cool to convert Micropolis to use GDAL's RasterBand datatype to represent the data on map layers. Since GDAL can read and write almost any kind of file used to store raster GIS data (and they have another library for Vector data too), you could import maps from outside of Micropolis to create a city on. Teachers could create and students could import a set of maps containing the local elevation, water features, land cover types, even current roads, population and zoning information where its available as the basis of a new city. From there they could play Micropolis as usual and manage and change their city as they wish, and it would be that much more personal and powerful! The set of maps that is used by Micropolis could be stored and loaded as a GDALDataset by quickly throwing together our own GDAL driver (or using an existing raster standard).