When investigating plan execution behavior, we sometimes need to review the information in the plan cache for a specific host regardless of topology.  To gather this information in a sharded cluster presently requires the user to connect directly to the member of interest to execute the relevant commands, which goes against much of our guidance to always connect to and query a sharded cluster via mongos.

Perhaps along with allowing $planCacheStats to target every shardsvr node (SERVER-45032), we could also allow the command to accept a hostname parameter when submitted via mongos.  This would allow us to collect the diagnostic information that we need without needing the users to connect to the shardsvr directly.