It's currently not possible to use $natural in aggregation to force a "natural sort order". However, if a user attempts a $natural sort when running the find command on a view, they'll get this fairly unnatural-looking error message:

> db.view.find().sort( { $natural: 1 } )
Error: error: {
        "ok" : 0,
        "errmsg" : "FieldPath field names may not start with '$'.",
        "code" : 16410,
        "codeName" : "Location16410"
}

We should consider whether or not to detect this up-front in order to produce a clearer error message for the user.