Instead of generating RDF dumps from the database, have a maintenance script that reads a JSON dump, and generates RDF output from that. This would allow use to generate consistent RDF dumps for various scopes, flavors and formats, with consistent data. It is also likely to be faster than loading entities from the external storage database (depending on FS access details).
As far as I can see, nothing happened here for a year. Moreover, subtasks are also dormant for a year. So it seems to be stalled. But if I'm wrong and something is happening here, please reclassify.
I think Wikidata-Toolkit could be used for that:
Obviously it would mean making sure the RDF serialization produced by it is consistent with what is being fed in WDQS at the moment.