Chris,
VMF is finally out in a draft form. You can define your own model source MIME type ("application/x-celestia-3d"?), and go from there. Thought it might help if you are still looking at an XML version of .ssc.
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Visual Model Format (VMF) is an XML document specification that is meant to provide a way of encapsulating multiple graphical standards within a simple XML container. More info here.