The movePrimary command will be deprecated giving way to two new commands called changePrimary and moveCollection.

Reasoning
movePrimary was mainly used by the users to move unsharded collections around the cluster since any unsharded collection had to live on the DBPrimary shard. Now that any unsharded collection can live outside the DBPrimary shard, movePrimary is no longer needed and moveCollection should be used instead.

On the other hand, since the user can still need to change the DBPrimary shard for other reasons than moving unsharded collections (like distributing the DDL workload across the cluster or moving the view's location), we will expose a brand new command called changePrimary that will change the DBPrimary shard and will move the untracked collections (not unsharded!) to the new DBPrimary shard.