It would be cool to have a device that instead of pixels, had bumps that raise up or down. Point the phone's camera at a scene, and you can 'see' the scene with your finger.
It would be very useful, but the display tech isn't there.
The state of the art are still two lines of text in fairly big braille devices (for ~$5k-$10k). There is some very interesting work being done at the University of Michigan[1][2] on a new mechanism based on microfluidics, bit it remains to be seen if that mechanism will reach a form factor even approaching a phone.
A few years ago Disney were working on simulating bumpmaps on touch-screens [1] using dynamic variation of friction achieved using electrovibration [2], but I've not heard anything about it recently. I wonder what happened to the research.
