The WikibaseRepo ItemVocabularyBaseUri service has the following TODO comment:

We currently use the local repo concept URI here. This should be configurable,
to e.g. allow 3rd parties to use Wikidata as their vocabulary repo.

We kept this comment while migrating the service to the service container (T277576), but we’re not sure if it still applies. The “local repo concept URI” part is almost definitely outdated – the code was changed from $this->getLocalEntitySource()->getConceptBaseUri() to $this->getEntitySourceDefinitions()->getSourceForEntityType( Item::ENTITY_TYPE )->getConceptBaseUri() in Cleanup repo Item vocab uri parsing & fix federated units – but does that mean that the TODO can be removed completely, or is there still something to be done and it should just be updated?

@WMDE-leszek and @Addshore would probably be the main people who know more about this.