In many cases servers could detect when they have different security configurations (-
rpc-encryption and -rpc-authentication) than other servers, or at least between tablet servers and masters. We designed these features expressly so that clusters could support a mix of optional and required, however this should only be the case while in the middle of a rolling restart to upgrade or downgrade the cluster's security.
So, we should detect these situations and either log loudly, or present some information in the web UI saying the cluster is in an inconsistent state. Admins who are in the midst of a rolling restart could ignore this, but it would give a heads up to everyone else that security configs are wrong.