A quick brainstorming:
a bigger lampshade splitted up in printable sub-components always ends up in freeform surfaces; for this application transparency /translucency of single shell is essential (single shell Thaulman-BluPrint or BioFila-silk really looks gorgeos)
ultralight body parts for RC-Models e.g. fenders, bonnets, wing-parts, etc.
flat-springs for vibration damping of mechanical components; e.g. suspension brackets
dust/moistur-seal electronic casing, with some sections printed single wall to allow shine-through of LED
to be continued ...