The way EntityChange is implemented is tricky to use and maintain. The deopendency on ORMRow seems to add a lot of complexity. The long inheritance chain ORMRow -> ChangeRow -> DiffChange -> EntityChange seems unneccessary, since all the changes wikibase needs to propagate are changes to entities.
A rewrite should result in a reduction in the amount and complexity of code.
We should also use this opportunity to move Change-related code into DataModelServices.