Several users have suggested a 'did not open' tab in the response section. This feature would speak to a somewhat specific use case in which the search and segment tool cannot provide an easy/accurate insight into a group of subscribers that did not open a specific campaign.
Hey Sam, thanks for the suggestion. This feature, as described, is not in the immediate plans for 2014. In general, an audience will have active and engaged members that are more likely to convert and our best practice suggestion is to focus greater attention on that particular segment. With that said, there are certainly use cases when considering the life cycle of a customer where you might want to send specific, targeted messages to members of your audience that have yet to do the action you intended, such as opening a mailing or clicking through.
We are considering some of those use cases as we plan our enhancements to our trigger functionality. One example could be to automatically trigger a related, follow-up email to all recipients of a mailing who do not open the original mailing within 72 hours.
We're going to mark this as "not planned" for now, but as we further progress down the automation path, I think we'll start to surface some useful tools around the use case you're describing. Thanks!