What would solve a lot of my problems with paper and current electronic solutions: Imagine some kind of touch mirasol with a matte screen and very thin body. You have a mode available where you can write on it with a stylus and can easily erase using your finger. As you write, you get instantaneous updates that simply show your handwriting, making it look very similar to if you had written it on paper. Certain motion…
The same applied to diagrams as well. Draw a sloppy box, and the Newton could clean it up for you, turning it into a vector image.
Everything was automatically saved---there was no "desktop" or "files" on the Newton (in many ways, it's the proto iPod/iPhone). What you are asking for is possible with today's technology, except for the folding bit.