Similar to SERVER-12583 which only checked for whether we thought the host was up or down. We should also check that other requirements of the read preference are still acceptable.

One complication that may need to be considered is what to do if there is now a "better" host that we should use. As an example if we were using PrimaryPreferred and settled for a secondary, should we unpin when a primary becomes available. What about hosts with lower ping times or that match an earlier tag predicate?