Kate McNeill from MIT pointed me to this interesting paper from the IASSIST Quarterly: Interoperability Between Institutional Data Repositories: a Pilot Project at MIT. (PDF format)
As Kate mentioned to me, this paper describes a tool which transformed DDI-format XML into METS, and it would be well worth exploring if this tool could be used in some way to support a deliverable on our EAGER grant: a tool which transforms DDI-format XML into FOXML.
Fedora supports several ingest formats, including METS and its own native FOXML, and so if there is already a tool that generates METS, that would be a good starting point for a FOXML version. Further, an interesting science experiment would be to take DDI, transform it both into METS and FOXML, ingest both objects, and see how if they would differ in any significant manner.