Imagine we can shoot a particle in a specific direction from a base interface. Normally we can't see this particle unless it's energized to a certain wavelength. Now imagine we can charge that particle such that at a certain time/distance from the source it enters and exits that wavelength for just a moment. Theoretically if we can do that often and fast enough then we can project images in thin air. This could also be doubled with some sort of laser beam to detect movement and it would even be interactive.
Now obviously we're still a ways from discovering this sort of function and making it viable for user consumption, but it would still be very cool.
I miss being off-the-wall creative like this. But then while it's fun it also not applicable.