I see the killer feature of 3D Touch on the iPhone to be the quick actions you can perform from the home screen. Good app developers will take advantage of this feature by figuring out what people do most in their apps and letting them accomplish them in one quick motion.
I can’t wait to see how 3D Touch feels to use in the real world. The ceiling on it is quite high, but I’m still worried about accidentally performing a 3D Touch action when I wanted a simple tap — I suppose I’ll have to experience it for myself. But I’m with Matt, this is a huge change for users and developers alike.