No fame, no glass, plenty of edge curling!
You can see examples of those hanger things in half the windows down at the mall. I would put the longevity in a house environment at a few years, tops. The edge curling increases dramatically with time as gravity stresses gradually concentrate on the center vertical portion of the print from stretching, as the edges curl. A bare print will also pick up everything that's in air from respiration by products to dust to cooking fumes.