'ceph-deploy install ...' is still an extremely useful tool to configure the correct repo locations for a given release, dev build branch, etc., and to install/uninstall/purge packages. As ceph-deploy fully goes away, we need to replace this functionality elsewhere. Perhaps, a new 'ceph-repo' command.
cephadm doesn't really require setting up repos. Maybe a simple script in src/scripts/setup_repos.py would be enough?