This fact that this object is Serializable enables me to return it from my RemoteDataImpl in RMI, but in local mode this is irrelevant. I just call getMetaData() and get the object.
No, it is serializable. You can try omitting this declaration initially, but eventually rmic will complain that it can't create a stub class for a Remote interface if a return value or parameter type isn't Serializable, or a primitive type.
Note also that nothing is actually serialized in local mode; the class just implements in interface that says it's OK if you do serialize it.