Going forward, there are some features I'd like to explore for XOM, post-1.0. In many cases, I'm not sure either how to implement or how to design them (or both). Otherwise, they just don't seem like core functionality. But here's some stuff you may (or may not) see in the future:
At least partial XPath support. This will probably be limited to location paths and possibly compound location paths, which is what people really need inside Java anyway.
Vector functions that operate on every node in a list.
Exclusive XML canonicalization
Document subset canonicalization
XML digital signatures