Yes, you would be surprised what you can haul with a low-enough gear. Think loaded touring! I have pedaled in rolling hills with thirty pounds of groceries or gear in panniers (including the weight of two racks and four panniers), in my granny gear, and I'm tiny and not particularly strong. I have a 19" granny gear on my Bike Friday -- thank heavens! When we did a self-supported tour in upstate NY, there were some very steep climbs around the Finger Lakes. I walked a couple of the steepest ones, it's true, but not many, and only late in in a 60+ mile day.
The key is -- let your DH carry the heaviest stuff, be it groceries, tools (on a tour), etc.!
Emily
P.S. That's a VERY cool bike!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow