Have you considered supplying an Ant task that will generate a subschema if generate a “Wantlist”?
An Ant task would be much like a makefile dependency. It would generate files based on input files, and update them when the inputs changed. An Ant task specific to subschema development would depend on some pieces not yet present: • A want-list specification • Loading of want-lists • A web services-based system, or other simple system, for generating the schemas automatically from the want-list Once steps 1 through 3 are complete, anyone would be able to generate such an Ant task, and we’d be glad to inform people of its existence.