Here's an idea for a product business with straightforward design requirements and a ready market: Modular display cases for collectibles. The collectible toy market in the U.S. alone does $1.8 billion a year, and the most passionate want to see their purchases at all times, designing their living spaces around their presentation.
Singapore-based Moducase serves this market with a series of stackable, modular cases made from aluminum extrusions (for the frame) and clear acrylic panels. Tiny, amiable LED spotlights and a "classy" black velvet base finish off each case.
The beauty of a modular system is that collectors can start small, then continue buying your products as their collection grows (and they always grow). The units can be shipped flatpack and user-assembled.
Check out Moducase's offerings, and see if you can do better, here.