Any chance you can consider adding an option to the RSS Feed settings that lets you prune them once they become a certain age listed on the forum in days you can set (change). But they are only pruned once that time passes based on having no replies. So any RSS Feed threads that do get replies made (at least 1 reply) doesn't get pruned. That way you can pull RSS Feeds onto a forum and keep them trimmed regarding how many stay listed on it, while still keeping the ones that got replies from members.
As things are now, which is usually the same case for most forum software that pulls RSS Feeds on a forum. You end up will thousands upon thousands of RSS Feeds listed that never get pruned, and most have no replies. But being able to set lets say a 7 or 10 day age period for old RSS Feeds to be removed (auto pruned) without any replies. That means you can always avoid having too many RSS feeds building up listed on a forum, while still retaining all those RSS Feed threads that do get replies from members (which of course you'd want to keep).