$natural hint is obeyed:
> db.foo.find({_id:1}).hint({$natural:1}).explain().cursor
BasicCursor
But $natural sort isn't:
> db.foo.find({_id:1}).sort({$natural:1}).explain().cursor
BtreeCursor _id_
$natural hint is obeyed:
> db.foo.find({_id:1}).hint({$natural:1}).explain().cursor
BasicCursor
But $natural sort isn't:
> db.foo.find({_id:1}).sort({$natural:1}).explain().cursor
BtreeCursor _id_