Developer Simon Gladman today demonstrated the use of the iPhone 6s display as a way to compare weights of an object, here denoted in a percentage of touch, on Apple’s 3D or Force Touch display.
The app called Plum-O-meter is currently a jailbreak option for tinkerers. I think it is unlikely that this will hit the Official App Store because it likely makes private API calls to acquire the data. However, it does show yet another device the iPhone can replace. Full video follows.