We believe it is the case that once a cursor is established on a node, the read preference does not play a role. For example, if a read preference "primary" query is sent to the primary and a cursor established, then that cursor can still be iterated if the node steps down between the cursor establishment and the getMore.

This means we no longer have to track the read preference during getMores, except in the specific case of new queries issued during getMores, such as described in SERVER-31665.