It has been some time ago, I had to use the Equinox Event Admin and DS implementation. That bundles (I have not checked other versions) missing the APIs - they contain only the implementation. So I have to create a splitted compendium myself to get them working in Karaf. I read this blog and I am fine, that such packages exist.
I do not see a use case for interfaces without implementations. But hey, it is up to you how you use this artifacts.
