Some new technical advantages:

1. Unicode
2. Better schema tools e.g. extension via namespaces
3. Better modularization tools: ODD genuinely does everything
4. Better integration with W3C standards (eg linking)
5. simpler, more consistent, data model

New/improved coverage or expressiveness

1. manuscript description
2. feature structures
3. dictionaries
4. prosopography and ontologies

(And P4 will continue to be supported for five years...)