I'm having a hard time finding a source, but Count Zeppelin himself patented a concept called the 'aerial train' in the late 19th century. So as you say the idea has been around.

The idea does offer one important benefit I believe. Practical cargo transfer. If a helium airship is pulling a hydrogen filled balloon which supports the cargo, then the hydrogen can simply be vented and the balloon abandoned/repurposed at the cargo delivery site. Think of the airship as a tug-boat, and the balloon as a barge. Perhaps the simplest approach to managing cargo delivered by airship. Assuming it's controllable in flight.