Some RSS Feeds are not well implemented, and contain a lot of historic items. It would be nice if there was an option to ignore "old" items, and only push items that are newer than the time of subscription.
This should be optional, so there needs to be a "switch" to enable this behavior. Probably within the !rss subscribe <feed URL> command. How about !rss subscribe ignoreOld <feed URL>?
If this is something you agree with, I'd be happy to provide a PR.