First idea:
Inspired by the music video for Warriors by Imagine Dragons, there is a sequence when lightning striking illuminates silhouettes otherwise hidden in the clouds. Recreating this in a physical display would provide a really dynamic feeling.
Second idea:
Illuminating etched acrylic from the side lights only the etched portion, and the remaining acrylic remains un-illuminated. Using etched portions of acrylic stacked on top of each other, an illusion of a dancing couple could be created.