The zookeeper stuff is not core-specific, it is at the top level just like CoreAdminHandler. I just copied the code from the jsp and have not really investigated – it only uses the core to get the ZkController: core.getCoreDescriptor().getCoreContainer().getZkController();
I'm fine with it as a RequestHandler, but this would require more crazy logic in SolrDispatchFilter like we have with CoreAdminHandler.
any thoughts? I don't use the ZK stuff (yet) so i don't have any opinion, but we need to fix some issues with this to get the new admin UI up-to-snuff