Today the CirrusSearch data pipeline can only ship updates to the content indexes. Future work with ores predictions requires the ability to ship to draft namespaces. Essentially this script will need to source a mapping from namespace to index (likely with unlisted namespaces going to the general index) for all wikis, and then generate updates with the appropriate index listed.
When doing this we will start shipping popularity score updates to non-content indices, before we allowed those to turn into noops at the indexing stage. To keep the status quo convert_to_esbulk will also need to throw away the non-content updates for popularity_score.