I use 3D touch all the time when editing text or changing settings in Control Center.
I have an older iPhone 5s and I use it occasionally and it feels weird to not have 3D touch.
I haven't used the new Camera UI in the iPhone 11, but it looks particularly ripe for 3D touch integration.
In fact I've always though the camera app should have had 3D touch integration. You could tap to focus and then continue pressing harder to take the shot.
And as far as discoverability, it's so simple. You just need a little dot of some particular color that indicates where you can press harder.
I can't remember which review it was in, but one reviewer said they were told by Apple that they discontinued it because they were never going to get it to work on the iPad and wanted continuity. First, I think Apple has tried as hard as they can to push the iPad and it has not replaced the Mac/PC as they thought it would. It has its uses. But it's not in the same success league as the iPhone and doesn't need to have parity in all features. Second, Apple has always said they're not afraid to make a great product that would cannibalize another product. But by crippling the iPhone, they're not making the iPad better—they're just making the iPhone worse so that they have an even feature set. Third, they do continue to have pressure sensitivity across a multitude of other products: Apple Watch, all MacBook trackpads, and the Magic Trackpad. You can even do pressure sensitive drawing on a MacBook trackpad. Fourth, the iPad already has pressure sensitive input in the form of the Apple Pencil in a way that is most suited for the iPad: drawing, which is not something the iPhone is as suited for. So why not let each be the best at what they each can do?
I've begrudged Apple for making lateral moves. Why do iPhones still start at 64 GB? Why do they still have USB 2 transfer speeds?
But this is regression.
Even if you wanted to go elsewhere in the market, they've probably patented it so that no one else can create such a feature. I've never heard of an Android phone with that feature.
It truly was an innovative feat of technology.
So much so that when the iPhone 6s came out Apple said it was the evolution of multi-touch: