The registry implementation is not completely out of the kernel. Some implementation classes are always present in the kernel. In the kernel, it should remain only the Registry interface.
For example, if I want to implement a registry based on a DHT framework as Hazelcast, I don't need remaining implementation classes.
As a new distributed registry, based on Hazelcast, has been introduced with Petals ESB 5.0.0, this issue will not be fixed.