Long persistence phosphors to make super-high resolution still photo displays
Right now the push in displays is all for computer and TV displays, with fast response time, and ideally in a flat form-factor. But these are expensive, really expensive if you want more than 2 megapixels.
What if we bring back an old technology -- long persistence phosphors -- and use them to make displays intended for still images, such as photography and art, at high resolution. They are cheap and bright. And if you don't need to do 60 frames/second, you can also get away with cheap electronics are more resolution per persisting frame.
It would be easy to start with black and white. B&W displays require just a screen of phosphor and a way to excite it. The resolution can be extremely high. Colour requires a shadow mask style technology, or projection such as CRT projection. A portal in the wall for say 10 to 20 megapixel B&W photographs and art might be a desireable product for the home. But there's hardly any limit for B&W.
There is a limit for CRTs, it get expensive to make a tube that big. New technologies are allowing the electron gun to not be far at the back so it need not be as deep as it is wide, but these are also heavy and fragile. CRT projection (mounted in the roof) might be a good answer.
There are however lots of ultraviolet phosphors which could be triggered by a UV laser or other such source, for rooftop projection or rear projection. If the persistence is long enough so you only have to do a few frames per second you can get in lots of resolution I would think. What would you pay for a 30 megapixel portal in your wall, one as sharp as a window (but not moving and only in 2D of course) showing scenes of the world, and great photography and art?