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.
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.
1: https://www.engadget.com/2016/01/12/braille-tablet-display/ 2: http://www.engin.umich.edu/college/about/news/stories/2015/d...
[1] https://www.disneyresearch.com/project/3d-touch-surfaces/