I'd like to have a way of loading document filters from externally generated sources. For instance, I may have run a clustering task over my corpus and the results may be stored in HDFS (Hadoop). A given cluster will have a centroid and a bunch of points that are in the cluster. The points are labeled by doc id (the Solr doc id) from the index.
Another example is I may have an external security system that can provide info on which documents are available to a user.