Say you wanted to get information about the picture of the day. As I understand it, you request action=featuredfeed&feed=potd, and parse the RSS or atom for item titles, then make an API query for further properties. But if featuredfeed provided a query list submodule, then you could use it as a generator to get any additional page information you want in a single API call.

Perhaps action=query&list=featuredfeed&fffeed=potd&ffprops=guid|title|link|description|pubDate could return the same information that's in the current RSS/atom feed. RSS is so 90s... :-)