There have never been any dependencies between units of different logical destinations. This means that the queues of the destinations are disjunct, and classic qRFC and the new bgRFC can exist in parallel without influencing each other.
A logical destination always runs in only one mode. The processing of the new units is delayed until all classic units that use the same queues have been processed for the same destination. There is no loss here, because these units waited in the classic procedure as well.
This procedure is realized by placing a unit in the classic queues that removes those locks from the new procedure that were previously created for all classic queues that were used.
This automatically synchronizes the classic qRFC with the new bgRFC. Units can be created in parallel in both procedures. The new units are not processed until the locks are removed since there can no longer be any dependencies on the classic procedure. This procedure requires an enhancement to the classic scheduler, so that the units that unlock the new queues are processed locally.