Haha yes then!
But they already add a body armor for hits coming at the back, and armor is much more useful against projectiles now. Shields also have much better armor values. I believe they should useful now.
I guess it is better for it to be this way, because when carrying a shield in hand an arrow might pierce the shield a bit and got stuck somewhere in the middle. It won't do any harm since there won't be any body parts just behind the shield. When the shield is on back, there is only 2-3 cm space between the body and shield. So it makes sence, in my opinion, for the shield to work as if it is an armor. Because it is technically no different than an armor piece that way, it is very close to the skin. It is like an armor reinforcement part.