Steve Jobs didn’t get everything right. When he stood in front of an admiring audience and gave them the finger during the launch of the iPad, he declared no pens or styluses are needed ever again. The vaunted Palm PDA with its little solid plastic stylus was dead.
Since then almost every major PC maker has introduced a product with a pen or stylus with every major device. Adobe introduced the Sketch, Sony and Lenovo use N-trig active pens, Samsung Galaxy Note phones have a passive stylus, HP just introduced two tablets with a Qualcomm Duet Pen, Wacom never stopped shipping pads with pens, and even Apple is rumored to be planning such a device. 
People (like me) still take notes using a pen and paper. Many people like to draw and/or do it for a living. Using a mouse or a finger can get you part of the way there, but when it comes to writing, for those of you who still know how to write cursive, there is no substitute for a pen or shape pencil.
The HP Duet Pen, the first to use Qualcomm Snapdragon digital pen technology on both a tablet and regular paper (it is included with the HP Pro Slate 8 and HP Pro Slate 12 tablets), allows writing (and digitizing) input from the device’s screen or via a regular sheet of paper using the HP Paper Folio. It’s similar in concept to the standalone product, the Livescribe pen, which digitizes from a paper tablet as you write.
Adobe’s Sketch is a prime example of an application-specific product targeted at designers and artists. Most of the other offerings, other than Wacom’s, are general purpose—if you offer it they will use it. Wacom, Adobe, and Livescribe are specific. Now HP is suggesting their Duet pen is also specific and is being targeted as a purpose-built device to mobilize the workforce and make (written) work sharable.
All this just proves one point: no one thing is ever the only thing, we need all things. Yes, touch is a great boon to the user interface, and so is voice recognition, and gesture, and so is and always will be the pen. And we will continue to use the keyboard and mouse, touch pad, roller ball, joystick, and even the VR glove.
Also, it is possible to replicate and, even in some cases, replace all those things with one thing, such as a touch screen, just like you can drive in a nail with a wrench—you can do it, even get the job done, but if you had a choice, would you?
When Palm introduced the PDA with a stylus and its clever writing methodology, it trained us. We had to learn how to make just the right swirls, strokes, and taps. It the same today with the touch screens, and the large display panels that weather broadcasters those who tally elections use. Voice recognition systems like Dragon are taught. They learn to associate the sounds you make with words. Pen systems have to also be teachable. That’s going to be tricky because, despite what you might have been led to believe about handwriting experts, we don’t always make our letters the same way. But the good news is we have so much computational power available in our devices now that they can be taught to recognize how, and more importantly what, we write.
The irony of this whole diatribe is that youth are losing the ability to write. Cursive is not being taught in some schools. Kids aren’t spending time in class learning how to draw circles and arcs so they can form perfect “ls” and “Cs.” They aren’t being taught how to hold a pen correctly, and how to develop the micro-motor skills in their fingers to carefully manipulate a nib. And why should they? Probably the only time they will use a pen is to sign a credit card charge, or maybe to fill out a form or two (usually using printing rather than writing).
So are all these marvelous drawing and writing devices being developed for a vanishing species, the old farts who can still write? Maybe the kids who like to draw? Personally I’m anxious to try HP’s Duet pen—for me it could be a productivity enhancer. But there may not be enough users like me to make a successful product.