Ideas for improvements to the discover plugin: (all names are open for improvements)
Add an est_release plugin, which would be used by the discover plugin to predict a release date for a given search entry. This would be an interface to media specific plugins, e.g. series_release or movie_release. Discover plugin would then check est_release(entry), and if a date in the future was returned, it would not perform a search for that entry.
A more generic rate limiting system would be in place for any entries that did not get a result from est_release. This would be an option given to discover plugin as an interval, maybe try_every, or some better name. Unique entries in the from section of discover would have their last search time recorded, and would not be searched again until try_every has passed.