Apple's 3d touch – an evolutionary perspective
medium.com
medium.com
Been there done that view is that this interaction makes difficult to have repeatable feedback from an app given fuzzy boundaries around what's long, what's short, what's high pressure and what's not.
The touchscreen may be very precise, but what about the fingers and the human attached to it?
We had synaptic measuring pressure sensitivity with accuracy for some time now, but adoption has always been a problem. It goes well with fuzzy apps like drawing, where feedback from pressure is immediate and visible, but giving two coordinates to a single touch and having no feedback is a pipe dream.
But hey nobody seems to care about accessibility anymore so meh.
I haven't looked into Apple's 3D Touch documentation very deeply, but the OS seem to respond, by default, to just three levels of pressure -- the first, the lightest, is treated as a traditional touch. The next level we might call a press, and is given an immediate "taptic" feedback, to differentiate from a touch. A "deeper press" gives another haptic response. In fact, it vibrates/taps twice as an error, if deeper press is not supported on the element.