Chess players struggle with board visualization and memory during games. A specialized trainer that presents positions then tests recall would fill this niche.
Build a web/mobile app that shows complex positions briefly, then asks players to reconstruct them. Include analytics on recall accuracy over time.
Premium chess training sites could license the technology or power users might pay a subscription. Start with a simple web version testing basic positions.
The risk is limited market size - only serious chess players would use this regularly.