Think for yourself!

Scratch your own itch While the business community talks about forming committees to standardize EDI B2B transactions, developers can apply XML to their own problems, building their own vocabularies to meet their needs.
Transformability XML's clean structures and accessible content give developers who solved one problem one way the opportunity to communicate with developers who solved their problems differently. Transformations from one set of structures to another is a common task in XML. Difficulty ranges from the trivial to the deeply complex, but an early focus on clean atomic structures can minimize these difficulties.
Version control Instead of binding your programs to APIs, you can bind them to document structures. Transformations can then simplify transitions.
Not quite conventional A lot of XML development thus far (notably Web Services) has focused on making it useful for people who just want to work with APIs and get work done the way they always have. It works, but taking a look at newer possibilities could give Open Source projects an edge.