I mean, if working with RDF has taught me one thing, it’s that converting between two different forms of serialization is trivial—it’s the underlying model that matters.

Exactly! And still, many who are in the integration business think that XML schemas is the only product required to exchange data between multiple parties. The serialization format(s) should be based on the use cases of the information. And even in a small organization use cases tend to pop up all the time demanding new formats. Most SOA-people see a problem with multiple serialization formats but I am thinking that it is almost insignificant these days if you have a well defined model.