The MongoProcessInterface type hierarchy contains implementations that aren't really interfaces to a process but rather to a particular cluster role that a process can act as (i.e. "ShardSvrProcessInterface, ReplicaSetNodeProcessInterface") etc.

In particular, we use "MongosProcessInterface" as the interface into the routing-role facilities of a node. In a world where mongod offers routing facilities (i.e. shards can act as routers), and not just mongos, this name doesn't make as much sense. It would be nice to rename/refactor the types to bring them more in line with how they are used today.