With the latest nightly and a sharded cluster, connect to a mongos server
mongos> db.test.insert({x : 1})
"_id" : ObjectId("5609546fc70c85ac8d3dc863"), "x" : 1 }
mongos> db.test.find().sort({'$natural' : 1})
{ "_id" : ObjectId("5609546fc70c85ac8d3dc863"), "x" : 1, "$sortKey" : { "" : null } }
QuInt A (10/12/15)
When sorting by {$natural : 1}, mongos includes the following element in returned documents: