I found another solution which seems to work - except of one small issue.
Instead of looking up the CXF bus, I expose now the DestinationRegistry configuration feature as OSGi Service, do the lookup for this feature and configure in each bundle a CXF bus using the shared DestinationRegistry.
The issue that is introduced now happens when I refresh the web context bundle which exposes the registry. Any bundle which registered at the registry is not notified and thus not updated. So every bundle has to be refreshed manually.
Peter
