Search Nodes do support sharding. For each shard in your cluster you will have a set of Search Nodes that handle the search component of queries.
To your point, we do not have “shard targeting” so when queries go to the cluster they will go to all shards.
Do you have a use case where you would need shard targeting and would you be able to share more about it? We would also be happy to jump on a call to go into detail. Calendly - Benjamin Flast