I had the same idea, I've even used it to move my duffel and ruck full of gear across campus, back when I didn't have a car.
Adding a longer pole to the handle bars to help steer and hold on to would have helped me. But the concept works really well for carrying freight as long as you don't mind moving at a walking pace or slightly slower.

Any other tips or ideas you can think of for making this work easier, maybe over rough terrain?