The ReadOnlyMode service currently requires LoadBalancer, which means migration to LBFactory/ConnectionProvider can't be completed in some cases.
Example: UserGroupManager
$this->loadBalancerFactory = $loadBalancerFactory; $loadBalancer = $loadBalancerFactory->getMainLB( $wikiId ); // Can't inject main ROM service, as this can be for a foreign wiki $this->readOnlyMode = new ReadOnlyMode( $configuredReadOnlyMode, $loadBalancer );