FYI: There is now a `--maintenanceMode` parameter available when starting a mongod as part of PM-2966
(All MongoDB clusters are sharded clusters). When --maintenaceMode=replicaSet, the mongod starts up in legacy replica set mode and skips auto initiating a replica set. When --maintenanceMode=standalone, the mongod starts up in legacy standalone mode and disables sharding and replication components.

Let me know if this is not the correct place to note that documentation changes are needed when PM-2966 is released.

Description of Linked Ticket

This startup parameter will allow mongod to run in the legacy stand alone mode without initializing the replication and sharding components.