A triple plus a wide range rear cassette yields a bailout gear. IMO, the ideal triple rear cassette setup is a 53/39/30 with an 11/23 10 speed rear cassette. We use that on the tandem for some rides. My idea of a bailout gear on the tandem is an 28 tooth rear cassette. However, I would go lower for 10% grade long climbs.

IMO, triple gearing can be tweaked by changing rear cassettes.

On Saturday, we did a ride down the California coast on Highway 1 with a Force 5 wind at our back. We had white caps on the ocean and we were easily going 30 mph on the flats increasing to 35 mph on mild grade descents. I was spinning a big gear even on the climbs. Who would want to spin 110 plus cadence for 1.5 hours? One the way back, we suffered immensely at 12 to 14 mph at high power and easy gears. My wide range cassette earned its keep.

IMO, one innovation that would be nice to have would be a quick release rear cassette. We carry a bag with 4 different cassettes and choose the right one for the particular route. The cassette comes off easily in one piece and the new one goes on. It takes 30 seconds max with no special tools. There is a mountain cassette, flat cassette and two in between.