Now this is pie-in-the-sky rambling, but we might be able to use Perforce/Hansoft to do the versioning/backup of the project. I teach game design, and we're implementing these technologies on our school. To my knowledge, it wouldn't cost the school any addition money in terms of licenses to create a community project, and since community outreach is part of our mission, the school might go for it. I'll need to ask around though to see if this is a possibility.

If not through the school, perhaps the Cartographer's Guild staff could create a Google community for it? Won't have as good versioning, but it would prevent catastrophic data loss.