I imagine an LCD (or equivalent) dancefloor that is pressure sensitive and reacts to the steps of the dancer with patterns or images. For example, each step might produce a ripple.
The images could interact with each other on the floor, generating new and unique combinations, depending on who is dancing with who.
By wearing a tag on each shoe (on hands for breakdancers), the floor could sense who's foot it was and give users custom patterns or images. A keen dancer may prepare a sequence or set of patterns/images in advance.
The images on the floor could pulse to, or be timed with, the beat of the music.
The LCD would obviously be protected with toughened, and perhaps frosted, glass.
The floor could also work for activities other than dancing, such as virtual football, where you stop the ball by putting your foot down next to it, and move your foot along the floor to kick it.
This technology would become obsolete (or at least less cutting edge) once holograms are mastered, whereby the dancer can interact with 3D objects (e.g. a holographic dancer).