The Rohloff enclosed-gear hub is an excellent solution for most tandem uses, especially travel and touring. However, some captains do not like the twist shifter on the handle bar as the means for changing gears. They would prefer to have a cleaner cockpit and a shifting action that more closely resembles what they are accustomed to on their chain and derailleur bikes. The same is true, by the way, of Rohloff riders on single bikes. The world has been waiting for the perfect solution to this dilemma, and now it's possible that perfect solution is at hand, in the form of the Gebla Rohbox shifting system.
The Gebla system replaces the bar-top (or bar-end) twist shifter with brifter paddle shifters and replaces the Rohloff gear box with a proprietary one.
If you think you might be interested in learning more about this system, here are a couple of resources you can check out: