HDFS-2231 started the process of adding configuration for HA, but one piece is missing. The current state of the configuration is, I believe:
dfs.ha.namenodes - a list of identifiers for HA namenodes
dfs.federation.nameservices - a list of federated nameservices
dfs.namenode.rpc-address[.nameservice-id][.namenode-id] - some specific config for the given namenode. If HA or federation is disabled, the extra components can be elided for backwards compatibility.
The issue here is that there is no easy way to discern which NN is paired with which other NN. Additionally, adding a new federated nameservice to a config will require changes to dfs.ha.namenodes which makes templating harder. It would be simpler to change dfs.ha.namenodes to be nameservice-scoped: dfs.ha.namenodes.<nameservice-id>.