I do quite a bit of work using just a stylus --- wrote out the paper for my TUG2003 presentation on a Fujitsu Stylistic PT-510 using a 3rd party handwriting recognition app:
http://www.tug.org/TUGboat/tb24-2/tb77adams.pdf
Recently drew up a set of calipers, did CAM, and sent the G-code to a hobby-level CNC machine to make a pair using my Toshiba Encore 2 Write 10 (while I have a keyboard for it, I rarely use it, and only use the on-screen keyboard when forced to):
http://projects.shapeoko.com/project.php?id=154
I see the iPad Pro as Apple's opening salvo in their return to pen computing (yes, I had a Newton MessagePad, yes, I've been trying to justify an Axiotron ModBook since they came out). Looking forward to the endgame (Apple Pencil having multiple buttons and is supported on other iPad sizes, the iPhone, iPod Touch and a slate / convertible MacBook) being more interesting than the opening move.