Let's say that I have a replica set with 3 members.

On that replica set I have part of a sharded collection and on that replica set it has 9 data chunks. All of the current read preference modes will pick a winner from the replica set and query all 9 data chunks on that server for a particular read operation.

It would be nice if an additional read preference mode existed that could see that it had 3 nodes and tell each node to run my read query, but constrain that query on each replica set member by a subset of the data chunks on that member.

Run query but constrain by chunks:
member1: chunk1, chunk2, chunk3
member2: chunk4, chunk5, chunk6
member3: chunk7, chunk8, chunk9

For some read use cases this could greatly improve read round trip performance by using all replica set members concurrently.