It would be great if there would be a feature (even experimental) that allows the interogation of Google Analytics’ and Facebook’s APIs to retrieve the number of pageviews and likes respectively for each post.
The information could be then used by theme authors or developers to build fast and reliable lists of popular posts or to further increase the relevance of related posts.
Popular posts, while a useful and desired feature, are usually hard to get right while in the Wordpress landscape plugins have made a mess of it, mostly by overcomplicating things. So people tend to stay away, but would likely gladly jump back in if done right.
With Google it would need authentication while with Facebook the data is public as json. As soon as the information is in the database, a simple query sorting by any of these fields, with or without time-limits, should be enough to build the list.
After years of experimenting I have settled for a plugin called Social Metrics that does cron jobs with the two services and updates the respective fields. Seeing how impressive Ghost looks already, the functionality of that plugin would be the only thing I’ll miss from WP.