MemberIdentifierImpl currently implements DataSerializableFixedID, but it has the same DSFID as InternalDistributedMember (DataSerializableFixedID.DISTRIBUTED_MEMBER). When serializables are registered in geode-core, that DataSerializableFixedID.DISTRIBUTED_MEMBER is associated with InternalDistributedMember.
Currently there is no way to deserialize a MemberIdentifierImpl, because nothing registers DataSerializableFixedID.DISTRIBUTED_MEMBER associated with MemberIdentifierImpl.
One option might be to have geode-membership register DataSerializableFixedID.DISTRIBUTED_MEMBER with MemberIdentifierImpl and let geode-core override it, but it's probably better not to associate the same ID with two classes. Instead, we should create a new id for MemberIdentifierImpl.