Apple's 3D Touch, introduced with the new iPhone 6s and 6s Plus, introduces a completely new dimension (literally) to interacting with the phone, by using pressure density, to add to the existing gestures made famous, such as Tap, Swipe and Pinch. At first, it seemed quite gimmicky, until you play around with it and realize the realm of possibilities available.
The taps are subtle, and by extending pressure, the app responds further, so you can feel what you are doing, as opposed to just tapping. A novel way of interacting, and the future of interfaces beyond iOS will certainly stem from this.
Apple have given us two types (or three really) of actions. The first is the 3D Touch from the home screen. You can have both static and dynamic popups that can arise from this. Apple have demonstrated this through their own bundled apps, where Mail for instance, hard-pressing would bring up Next Message, Search, VIP Messages and Inbox.
Looking at the Phone app, you get a more dynamic experience. You get a list of the most frequently called contacts (actually it is a bit more sophisticated than that, it determines based on time of day whom you call more frequent). If you think of Foursquare, you can hard-press to check-in quickly, but the point being, it is a great and intelligent shortcut-enabler.
It's important than developers start to embrace this right away, because the more third party apps starting using it, the more the users will expect to hard-press and get some sort of feedback. Evolution will make this an expected behavior.
The most obvious initial benefit of 3D Touch were to designers and artists, using drawing apps like Pixelmator, can press harder or softer to get a different brush strength. This brings a much more intuitive and realistic experience to drawing.
Pop & Peek
Not the names of breakfast cereal characters, Pop & Peek are the two other features of 3D Touch that Apple have demonstrated. Within an app, you can firmly press to get further contextual information, called peeking.
The user would then be able to commit to the actions by pressing even firmer, or un-commit by pressing less-firmer or removing his or her finger. Apple have shown in their apps how this works. In Pages document viewer, you can preview a document without having to open it by peeking, you can firmly press in Music to see inside an album (the tracks), and in Maps, by being able to put a pin down by pressing firmly.
We have also seen other 3rd-party apps slowly integrate this, although at a slower pace. However, pop & peek should be considered a far greater UX design revolution, as can be used to change how we interact with apps more significantly, rather than superficial peeking.
A new Navigational Paradigm
Some UX advocates have recommended putting the navigation bars on the bottom for greater ease-of-reach, whilst many have began to better support landscape mode, so users can hold their phones in landscape mode. Introducing 3D Touch, literally adding a new dimension to UI navigation.
The introduction of the larger iPhones last year has meant it is no longer comfortable for users with one hand to be able to reach to the top parts of the screen. Sure, some UX designers suggest putting navigational buttons at the bottom, similar to Tab bars, but another option could be to be positionally agnostic, to use 3D Touch as a way of allowing users to navigate by pressing anywhere on the screen, dimensionally-distinguished from the superficial navigational elements you see on the screen.
Whereas swiping allows you to go backwards and forwards in a navigation stack, hierarchically, 3D touch could provide popups that would allow users to navigate in non-hierarchical ways, the same functionality provided in a Tab bar, where related but not sibling screens can be navigated to.
Whilst popping a navigation-based view (going backwards) has been a standard on iOS, by swiping left-to-right, if you add any buttons on the right of the navigation-bar or toolbar, requires over-extending your fingers to reach. 3D Touch therefore presents a new way of getting to that button function, by force-pressing anywhere on the screen. If you aren't implementing Peek-and-Pop, you can allow your view to support 3D touch to bring up a contextual pop-up with greater options.
We have already had the first taste of this on the Apple Watch, with Force Touch, which is a similar concept, the ability to press hard to get a contextual menu, Evolutionary, users will start to anticipate and expect other ways of navigating that isn't visually obvious, but implicitly intuitive through training and daily use. We will feel, intuitively that we can press and navigate.