In China it is very common to see a passenger sitting on the rear rack and, in fact, many bike have a cushion seat attached to the rack, such as here:
One thing you will notice in China is that it is very common to ride sidesaddle. Particularly for women. My friend almost always rode that way and that is also how my daughter prefers to ride. When she visits me in the States she doesn't ride that way often because it is illegal in The US