How far an application is backward compatible depends on the way it uses hivemind. For example a web application that uses the HiveMindFilter for loading the registry and defines service and configuration points without any complex schemas or factories has a good chance to be 100% compatible.
Things that have changed
The registry build and construction process
Unique attributes and key-attributes
Configurations no longer limited to lists
These interfaces have changed. Items that were of type java.util.List before are now of type Objec: