I just stumbled upon a CNET news article about researchers working on an app that could potentially remove the need for a wireless Braille display.
The app would allow people to use Braille directly on a tablet's touch-screen.
According to the article, the app would have eight keys (similar to a standard Braille keyboard) which would not have a predefined position, but rather work with the location of the fingers. A user simply presses eight fingers anywhere on the screen, and the keys are automatically oriented to that location. If there's a problem, users simply lift their fingers and put them down again.
I am not a Braille user, so don't know if this is something with real potential, or whether it has too many limitations to make it usable (for example the article observes that there is no mention of haptic feedback). However, the financial implications of having a software alternative to expensive hardware certainly makes this a project to watch.