With MongoDB we can create tags sets as explained here Configure Replica Set Tag Sets
By doing this, we can address writes and reads to specific members in the replica set. It is also possible to optimize and distribute our indexes across the members, depending on the type of operation we want to execute (reads / writes)

MongoID only allows to define the same set of indexes for all members in the replica set. It would be great to be able to define different set of indexes by members in the replica set based on the tag sets that has been setup in the configuration.